AI games can be things like team survival games. Some of those games are posted to YouTube. People care enough to put the videos online, that means people care about the games. Maybe very few people, other than the players themselves, care about solo games involving AI. But you can't say as a general rule that nobody cares about AI games.
The cost of making a backup of the games before deleting them from the server is minimal. What even is the cost of 300GB of cloud storage? Just save them somewhere. Maybe in 5 years the cost of storage will be so small that we can restore all the replays to the server at basically no cost. Or some other way to make the replays available. There is no good reason to delete history even if most of the history is crap. Once it is deleted we can never get it back.
Do we even have a complete backup of all replay files? Just load them into a single 1TB drive and send it to a FAFer's house. 1-2 copies like this would ensure that history is not lost.