Ignoring the lack of updates if the game is buggy, games back then were also more focused on quality and make gamers replay the game with unlockable features based on skills, not money. I can't count the number of times I played Metal Gear Solid games over and over to unlock new features playing the hardest difficulty and with handicap features, and also to find Easter eggs. Speaking of Easter eggs, you'd lose a number of hours exploring every nook and cranny finding them!
Games were definitely buggy and I honestly think people forget how much better the quality is nowadays.
I also think there is something to it just being the 90s or so and not having much choice. If you only have one game to play then of course you're going to replay it to death. If I have a steam library of 1000 games then I'm much less likely to.
A lot of this is just nostalgia for the past and the environment as opposed to games being any better.
Absolutely. I enjoyed and played a lot out of King of Dragon Pass back in the day. Yesterday I sat down to finally play its spiritual successor Six Ages: Ride Like the Wind. From what I remember from KoDP it plays exactly the same (at least during the first hour). Yet I couldn't force myself to keep playing it. Same way nowadays I can't seem to get hooked with genres I used to play a ton as a kid: RTS games like Age of Empires II and Warcraft 3, life sims like The Sims, point & click graphic adventures like Monkey Island, traditional roguelikes, city builders, etc. Other genres I try to get back into and I do manage to play a ton of hours of but I'm never able to finish like when I was young (e.g. JRPGs)
When I try to play many of those games I tend to feel kinda impatient and wanting to use my limited time to play something else that I feel I might enjoy better. A good modern 4X game with lots of mod support like Stellaris or Civ6 instead of RTS games which have always felt a bit clunky to me. Short narrative games like Citizen Sleeper or Roadwarden instead of longer ones I'm not able to finish. Any addictive modern roguelite, especially if it features mechanics I particularly like (like deckbuilding and turn-based combat). If I ever feel interested to play a life sim or a city builder nowadays it has to feature more RPG elements and/or iterative elements and/or deckbuilding and a very compelling setting to me. And so on.
It feels like many of the newer genres (or the updated versions of old genres) are just more polished and fine-tuned than genres that used to be popular in the 90s and the 2000s. They just feel better to play. And to be fair in some cases they might be engineered to be more addicting, too. Like, I did finish Thimbleweed Park some years ago but I feel like nowadays no one is going to play witty point & click graphic adventure games with obscure puzzles if they can play a nice-looking adventure game filled with gacha waifus.