"What is the appeal with books that are this old?"
Not very often from what I can tell. I do see the sentiment you've expressed regarding games much more often. Why is that? I'm not sure. Perhaps it's just a sign of the immaturity of games as a medium (compared to books, anyway).
There's a lot of experimentation in old games about how to approach certain concepts, where eventually something won out and became the way we do it. So it's very strange to go back to e.g. an old first-person game and realize that WASD controls aren't used.
I recently saw this YouTube video ("How System Shock's Reboot Wrestles With Adapting Its Legacy" by Errant Signal) that talks a bit about this take on the issue, which might interest you: https://www.youtube.com/watch?v=YDQ24iAkh90
I would argue the age of a game is entirely orthogonal to whether it is possible to still enjoy playing it.
Will EVERYONE enjoy playing it? Probably not. But some people do. And that's enough to give projects like ScummVM a valuable purpose.
Games are entertainment. So they are supposed to have higher levels of engagement over time
In a way it's like asking why people read old fashioned novels, even though they're out of step with modern language and culture.
Some time around 2014 I finally got around to playing Castlevania: symphony of the Night. It was almost 20 years old, casykevania had long since moved to 3D graphics and stages. Even when it was released in the 90s it could have been considered outdated due to its small, sprite-based graphics.
It turns out, the game is a masterpiece. The control, the level design, the progression, the exploration, the freedom of item choice are all exceptional. Even the graphics are beautiful for what they are without needing a RTX 4090 and 4K display. I’ve replayed it several times since then and it opened up a new genre of games that I hadn’t previously considered liking.
Many of the Lucas Arts point and click adventures may or may not soar the same interest. They’re quirky, funny, clever games that can be played casually.
For kids who like games, the gameplay is enough. They might say how dopey it looks at the start, but if it hooks them, that reaction will fade away.
I have a hard time finding the appeal for myself.
It doesn’t have to be all about high-end graphics.
Plot, game play, fun is what’s most important for a large segment of gamers.