Okay.Not sure what you don't get about it. When I was a kid growing up in the 80s and 90s there were thousands if not tens of thousands of games already out that I just never had the time to play but still wanted to play. Now I am in my 40s and have some free time and its great to go back and play some of those games from back in the day. There are also games that I loved when I was a kid and its been 20-30 years since I last played them.
Then you take someone like my nephew who is 13 and is loving playing through all the old games that came out decades before he was born. What's more he loves sitting down with his father and myself and playing some of our favorite games from when we were young.
I mean have you never seen a movie or show more than once or read a book a second time ?
There are a gazillion games, that is true, most are bad Nostalgia makes me want to replay some of those that brought much joy when growing up. But there is no Atari 2600 game I probably would play to day, exception might be space invaders.
As for C64 I have tried a bunch due to nostalgia, again they are usually not that good, but I loved them then and in retrospective view, still love them for what I got from them then.
There are some classics of course, but like books and movies very few stand the test of time. Which is why I do not get the, lets play this ancient game that has bad mechanics, feedback loop and what not.