One reason will be memory related. 32bit can only access so much, whereas 64bit isn't anywhere near its max yet. This applies to both ram and storage.
32bit max Ram is 4gb whereas storage is 2.2tb... sure, most games don't use the storage amount but that ram amount was restrictive 10 years ago, yet alone now.
Meanwhile, 64 bit max memory is 16 million terrabytes. Max storage size of the drive format that 64bit supports is 18.8 million tb but windows itself doesn't extend to all of that, so the 16tb is all you get. I guess they giving themselves space to grow.
Right now you can't install anywhere near that much and windows can't access it anyway -
https://learn.microsoft.com/en-us/windows/win32/memory/memory-limits-for-windows-releases - max is currently 6tb in some versions and 2tb in the more common versions.
I expect most games now are 64bit just to access more ram.
Most PC hardware has been 64bit for 10 or so years now. AMD made 1st one in 2003 but obviously it took a while to catch on.
Indie games will be the ones using 32bit longer.
Then it would depend on when/if Windows stops supporting it. That will happen eventually but as there are so many programs written as 32bit versions, its not going to happen for a while for backwards compatibility reasons.
Microsoft could release a 64bit only version now if they chose to. Its possible the 64bit version would be smaller as there is coding in windows to cope with 32bit and 64bit drivers as well. It essentially has 2 copies of a stack of files just to be able to run both.