Some old games really are better if you like a certain type of game mechanics. For instance if you like crpgs with tactical combat there just isn't much being made like that now. The console gamers prefer a different type of game and that is the type that is being made now most of the time. Faster, twitchier, and imo more repetitive. Popamole. I guess it's really more about faster non-tactical combat that is the problem for players like me. I prefer combat that is more like chess where you have to carefully consider all of your moves and search for an optimal set of moves to win.
I am currently playing Icewind Dale for instance. If you like that type of game there really is not much out there anymore. I have had to resort to replying Infinity Engine games like Baldur's Gate II, Icewind Dale I and II, Planescape Torment, Temple of Elemental Evil, Fallout I and II, and Arx Fatalis just because these sorts of games just aren't being made anymore. I suppose the most recent games that I like are Neverwinter Nights 2: Mask of the Betrayer and Fallout 3: New Vegas.
I can't speak for everyone, but I don't have any nostalgia for games just because they are old. I don't seek out the first games I played from the late 70s like Super Star Trek that I played on my friend's DEC PDP-11 or text adventures like Colossal Cave or Zork or Atari 2600 games like Adventure or Combat. I don't care about the games from the early 80s like Archon, Castle Wolfenstein, Crush Crumble and Chomp, and Choplifter either. Yes I used to love playing them. They were fun to play at the time when nothing else was available, but I would have much rather played modern games with their far superior graphics. There are games that I know I would enjoy replaying but can't due to the graphics. Might and Magic 6, 7, and 8 for instance I used to really enjoy but can't anymore and of course games like those are not being made anymore either.
Only certain types of gamers are being catered to now. Only certain play styles. If you are not one of those people you have no choice but to replay old games if you want to play computer games at all. It's not nostalgia. It's desperation for any computer game you can actually enjoy and that means saying no to popamole twitch style combat if that isn't what you like. If I actually want that style and sometimes I do it is easy to find, but what about a more thoughtful style where you carefully plan your moves? You just don't see it much at least in crpgs.
There are some smaller independent and mostly crowdfunded developers now that are at least claiming to try to cater to that style of play but so far there hasn't been much in that regard and at least one attempt, Pillars of Eternity, failed utterly in terms of the combat imo. It ended up playing more like Dragon Age: Origins or other modern Bioware games. Again, catering to what the majority of gamers like despite being funded by gamers like me who wanted something that played more like Icewind Dale or Baldurs Gate II.
It is unfortunate that some developers seem convinced that nostalgia is everyone's reason for replaying old games because then you end up with games that intentionally go backwards and try to emulate things that were done solely because they had to be done that way because computers were so much slower or because rendering techniques at the time just weren't advanced enough. They are copying not only the good things about the older games but the limitations as well. I'm sure the developers who actually made those games would have loved to have been able to use more realistic graphics and smooth, continuous movement, but they didn't really have the choice back then.
This is the danger of attributing our love for older games to nostalgia. Maybe for some people that is all it is and they are perfectly happy with modern games, but that is not always the reason.