Libraries like libpq.dll and libmysql.dll started to drop 32bit support, and older versions start to introduce security issues through dependencies. See #2022 for examples.

I asked HeidiSQL users in May 2021 whether someone still needs 32bit support: https://www.heidisql.com/forum.php?t=37945 . I had a look at the statistics at that point, and found roughly 1% of all users were on 32bit.
Now, 3 years later, we have roughly 0.5%, so even less.

Note the portable package may still continue to be shipped in a 32bit version, but with a growing amount of outdated and probably insecure libraries. This was also mentioned several times as a possible alternative for the few ones who need that.