Without any questions asked? None.
There are always some questions in regard to newly released games (does it run on my system? is it bug-ridden? what's its price?, etc.)

Apart form that: pretty much every old game that I have fond memories of.
Nostalgia is a bitch.
But again: with the price as a definitive decision maker.
Too expensive means no day 1 purchase from me - no matter how much I love a game.

And for new games goes the same, of course.
Let's be honest: I am spoiled by today's permanent discounts.

The recent prices for new games (€50,- and more) are simply too much for digital downloads only (for me at least) - despite the fact that they are actually cheap in comparison to the prices I paid in D-Marks for games in the 80s/90s.

But again: back then I received a nice box, one or more diskettes/CDs/DVDs, and (sometimes at least) some physical goodies for that price.

none

Buck Rogers: Countdown to Doomsday
Buck Rogers: Matrix Cubed

I love the SSI Goldbox games and I love old pulp sci-fi. Put them both together and how could I possibly pass that up? I know they're available on abandonware sites, but I'd love to see them officially re-released here on GOG.

I didn't mention the Remastered Collection because those games weren't made by EA, and they could've touched up the AI at least a little instead of just upscaling everything to take 32 gigs and require modern hardware, but it wasn't as bad as Reforged or many others I could name, they added console missions and made some quality of life improvements, so all in all it was a decent and worthwhile, if conservative remaster.

Hey, I actually liked Dragon Commander. It's something unique: a mix of turn-based strategy, RTS, RPG and a TPP action game. It even has elements of a card game. I've never before seen such a mix of genres and IMHO it's very good given how much different elements are incorporated into the game. Larian is better in doing classic RPGs, but Dragon Commander is really fine!

Sure, I liked it as well. It's more the case of - they have this amazing idea for a game, they have the right people and tools to make it an unique masterpiece and cult classic, and instead they make a decision to rush it out, as cheaply and crappily as possible, cutting all features they could down to the plot itself - all to fund a bland and unremarkable game they could've rushed at much lesser expense and effort instead to fund the Dragon Commander, as they initially planned. Moreso seeing as they could've doubled back and made another OS game to their liking if they were so inclined, and nothing would've suffered for it.

I don't consider 50-60€ too much for a new game. That doesn't mean I have to buy them at those prices - not anymore.

If your earnings / bank account are big enough, the original question becomes irrelevant.
If not:
- Replayability: If you're going to put 1000s of hours into one game, then why not? (not my thing)
- I can't think of any reasons (for me) to pay the Day 1 price. There's no limited availability anymore, and there are A LOT of cheaper alternatives ("older" games).

If you look at the sales figures of triple A games; many people seem to buy them early, at day 1 price. I wonder if there's a main reason/motivation for that? Peer pressure? The social aspect makes sense for multiplayer games, but for single player games?

Buying a game without researching it first is another matter.

Why?
(a question not only aimed at you)
Not why those specific games; why pay the day 1 price for them?

ps. I'm not insinuating that there's anything wrong about it; I'm just curious about other people's motivation(s).

Was it even possible to buy?

Yeah, on Steam.
It was released on Thursday.

Getting really good reviews, but that's mostly from MP gamers. If the SP campagne is short, which I'm guessing it is, I'll pass.

I'm assuming Day 1 is of GOG release, not necessarily a game release. This means, of course, a DRM-free release

In that case I would instabuy in no particular order:

Skyrim
Anything Far Cry
Red Dead Redemption I and II
Mass Effect games
NieR games
Death Stranding games

There may be others but these are the ones which come to mind right now.

Why do you assume that? The OP only lists games that haven't been released, at all, anywhere.

to a lot of people there is only one place to buy games.

i used to be one of them

I see no reason to think that the participating people here only buy games on Steam.