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Mostly this.
Permadeath works best when the game is built around that expectation, so no repetitive start sections or similar, generally shorter games (though longer isn't all bad, traditional roguelikes tend to be quite long, I think my one winning run of ToME took 30 - 40 hours) where you either gain something from each run or learn and improve your skills so the next runs become easier.

But I also find it adds a certain challenge to games too. For example on a recent run through of Crusader Kings 2 I decided to do it on Ironman and it was so much more fun knowing that I couldn't just save before going to war and reload if things don't go my way. It gives everything a bit more depth as your decisions really matter.

Some games just absolutely don't work with permadeath, and one that I was looking forward to and expecting to love but didn't was Sunless Sea.
There I felt that the game set up didn't really work with permadeath. Dying was very easy and not a lot carried over to your next run, which then involved repeating the same set of steps to get re-established. I loved the world but quickly became bored with dying and not being able to experience all of it.

So I generally like permadeath (and roguelikes) but (like most things) it works best when it's done right.

In my opinion permadeath should have some kind of progress or getting back things that you have already had, otherwise the player will lost their interest.
Either family tree progress in which player can develop or invest in his future character or time progress in which bosses, character who were killed are still dead or unlocked locations, items are still unlocked and maybe you can find corpse your previous character with the items or kill the monster to get them back.

The new trend is probably due to over-saturation of "rogue-likes" in the market on the back of FTL's success. Personally speaking, unless the game has some other appeal (eg, Don't Starve's humor) I generally avoid rogue-likes. I understand why some like it, but one man's "hardcore respawn challenge" is another man's "instead of putting more content in the game, let's just recycle the gameplay itself into a string of sub-games" which to me, often feels the cheapest way of all of adding difficulty / artificially padding out game length (even without single-slot, checkpoint-only saves being far more a fragile negative than a positive when a game crashes / hits a game-breaking bug that ruins not just current run but all runs)...

After losing a game (forgot title) once due to force majure (I forgot why, maybe pc crashed, maybe loss of power) and losing a big chunk of game time in a run going well.... I am not really buying new games with permadeath nor choosing ironman/dead is dead option in the settings. Even if your computer is rock stable and you have a UPS, there are things like children or animals jumping on your keyboard, Windows 10 deciding to restart RIGHT NOW and things like that.

Before someone says something, yes I have accepted gifts, at least FTL comes to mind. I should start a new game in there as my first run is stuck in a fight I cannot win. Maybe let the enemy kill me slowly just to hammer home the importance of having a high damage gun.

What about games where dying is a major setback, but sometimes recoverable? (I'm thinking along the lines of Wizardry 1-3 and 5.)

Or just fly away as soon as your hyperdrive has charged?

IF I can survive that long. I would still need to get a better gun very soon or dead I will be.

Cheat codes were once a thing. Nowadays they have often been replaced with your credit card number. You can also often find a trainer (beware of malware) or learn Cheat Engine.

I sometimes want to finish a game even if I have to to it through godmode.

It wasn't so much a "here's what you should do", but rather a "here's what I do".

depends on the game, where its your main and you lose everything it can ruin my day so i avoid them, yet i love permadeath in games such as project zomboid or xcom, it really hits you in the guts when you lose a char you have history with. in those cases the stories continue on, characters are part of the story not the integral focus tho. its not game over when they die

If permadeth is a set back (losing a unit in a bigger strategy game), I'm perfectly fine.

If permadeth is part of the design, intended as "death part of moving the game forward", that also is ok (and often scripted). Unless become a complete chore and waste of personal time, that I never asked developers to waste (I.e. Dark Souls).

What I found reducing the fun/relaxing factor is when you don't have;
1) option to opt out from permadeath
2) dying is 100% going back a few hours of gaming and/or start from scratch.

How much of this "Permadeath" wave is tied to the new feeling of Retroism, more than strong, meaningful, design decisions?

Fair point, but forcing the permadeath gamestyle on everyone is pretty much the antithesis of choice, unless that choice is to not play the game in the first place, which is detrimental to a small company heavily relying on sales of their games!

This, I don't want to waste my time losing everything that I've worked for!

Permadeath can be fun if the game is designed around it. Like in Don't Starve you usually learn something with each new attempt.
I agree that it really can add meaning and weight to decisions.
But I would never play iron man in long games which rich story (like a classic RPG) because losing and starting over after maybe 150 hours and then do everything all over again? No thanks.
I think that's why "Rogue-Like" is always randomly generated in some way - to keep the boredom at bay each run is different. Much like 4X games where some mistake in the beginning might come into play 10s of hours later when it's too late to correct it. New game -> new experience.

I personally am more of a story gamer and so I avoid permadeath games - I played a bit of Don't Starve and liked it "objectively" but when my survival skills went up it was too much to do stuff (base building etc) all over again every time and without a real story to follow I just couldn't muster the patience over and over again (actually the funniest runs were when I died very early for some stupid mistake).

A few years back I was working on an AI DM who would build a story from tiny fragments and characters with more or less random follow-ups building an actual story arc with side stories and stuff like that. I even had a (very primitive) prototype (in C#)... lost the code though. Maybe something like that would make me keep playing...

Two Worlds 2 final battle anyone?

How about permadeath for the gamer!

Now that would be a challenge! :D