I still check it from time to time, and now it redirects to the main page. Can someone clarify this situation?

Yes it is:-
https://www.gog.com/forum/general/gog_connect_is_it_dead/post15

It's been dead for a while, they simply took down the link recently.

Well, that is very strange. Why then its page was up for almost two years after its supposed death, not reflecting that fact in the slightest? And also I'm not sure that the post you linked actually answers my or topic starter's question. To quote: "GOG Connect offers were time-limited and are no longer supported." This can be interpreted in a way that yes, sure, every one of the offers was time-limited, but after their expiration something else always would come.
There are many posts after that answer you've linked, but instead of clarifying the situation, the same GOG team member just closed the discussion after a while. Even if this answer was given by a GOG team member, this is not official enough, I guess. Since there's no big announcement and just some reply deep inside the forums, it leads to spreading rumors and nothing more. The only info you can google is rumors and general talk on reddit like "well, it's probably dead".
I mean, it's not as embarrassing as Google Stadia and any official announcement should end this uncertainty once and for all.
Again, "they simply took down the link recently". I guess they just forgot the same way they forgot to check if a certain game actually works without GOG Galaxy and doesn't automatically install a rival launcher on first launch (I'm talking about a recent Saints Row 4 update, which I got through GOG Connect actually).

P. S. I guess they don't care about the forum either. The slowest and the most outdated thing I saw in years. Successfully posted this message after 5 attempts and a browser switch.

I gave up on GoG Connect about a hundred years ago. It's never worked for any of the several hundred+ games I have on Steam. I wouldn't even mind paying a GoG Connect fee per game to get various games from my Steam library on GoG, if it was infinitely cheaper than buying the game again on sale on GoG. Gotta have those DRM free versions of my favorite games. You're not the only one, I've been experiencing this anomaly where I can't wishlist games or post reviews, it asks me to log in when I try to do either, even know I'm already logged in. Literally nothing can fix this. It's f***ed.

Like, they're actually losing sales from me.

Because I can't f***ing WISHLIST GAMES BECAUSE COOL GLITCH THEY REFUSE TO FIX OR HELP ME WITH, BRO.

I guess they don't advertise it, newsletter it nor post about it because ... it's like with delisting of games I reckon. It has negative connotations. Although there are some who are happy about the Connect dying, so maybe it wouldn't be such a bad press. Saying nothing about it is kinda weird though and people notice such stuff adding up with time.

Speaking for myself, as I use only Steam and Gog - I don't really doubledip between those two, except in rare cases, so it's not like connect was stealing sales in my case. I get the game where it is cheaper, has more features, is less broken and is more convenient to play in general. I mean, buy a game on gog that has online co-op/multiplayer... good luck finding a match among all the galaxy-phobes and collectors who don't play anything anyway.

Yeah, GOG Connect is not accessible anymore. I agree that there should be an official announcement of any sort about that but no word about it at the moment. Previously when it's still active, GOG Connect gave me a choice on how to play a game without paying an extra dime. Say, if I have Deponia on my Steam library and do the GOG Connect kind of thing (when it's offered), I would also have it on my GOG library. That way, I can launch Steam to play it, but also, I have the liberty to carry the game installer to any computer I wish to play on. But that's simply arguable anyway.

Not that strange really, and even though we no longer see the link, I'd be very cautious about assigning to oblivion forever, as the page may simply be hidden/disabled, until they are ready to use that form of promotion again.

And when you consider how nearly every month someone starts a thread querying about the state of GOG Connect, it is easy to understand why they eventually removed it. The only question maybe, is why they took so long? Maybe they hadn't made up their mind sufficiently or had thrown it into the too hard basket until they were ready to focus on it and come to a decision, or maybe they decided to make it a New Year thing.

Nothing means it won't come back, especially when we haven't had an announcement. Maybe they are revamping it and are going to support Epic instead. Or maybe, just maybe a big change to the forum software is coming, and they are tidying up loose ends to make less transfer work.