Alright, i don't have experience in uploading different builds of my game on here, so i just assumed from one of the topic i linked :)
But my point still stands: the uploaded builds are not *tagged* as working on a 32bit or 64bit architecture.
Here an example: 
Here you have a bunch of different builds, named by the developers as working for windows, mac or linux... but as you can, the 32bit and 64bit architectures are not differentiated by a little badge like OS are. Allowing this tag would be especially useful for indie games with a single build (which are legion here) which are most of the time just named after the game itself.
Another example here: 
See ? as a gamer i cannot know if this game will work on my 32bit architecture.
If itch.io adds a tag for 32bit or 64bit games, it will at least raise attention to the devs that this difference exists, because right now i bet most don't know this is a crucial difference.