Currently, there aren’t a ton of games that regularly need 32GB of RAM to play. A few new games like Star Citizen reach that level of demand. In most cases, you only need 32GB of RAM to play a game with very high graphical settings and/or to manage lots of multiplayer or simulated assets at one time.
While most modern games will technically run on 8GB of RAM, to have a smooth experience without much video stuttering, most AAA titles from the past 5 years are better off with 16GB. If you need to host a server or want to stream at all, then 16GB of RAM is pretty much the starting point and can go up from there.