I've never understood why people would have more than one page for more than one version of a game. This site lets you upload multiple builds at once, right? And yet, I still see people post separate pages for the Android and Windows versions. Without naming names, one game I've seen has one whole page for every demo build of the game they have, and each of those pages are so barebones that they might as well have condensed them all into one concise page. 

Was there ever a point when Itch didn't let you have various builds? I know one guy who did it who simply didn't know about the feature.

There generally should be no reason to make multiple pages, if you see it happening it's maybe because the person who made the pages wasn't aware they could have a single page. 

There are some practical reasons to having multiple pages, you can mange two different sets of owners. I don't think this is a common case though.