This is tougher than it seems on the surface.
A few years ago, I was involved in planning and running a maker "fest". We invited makers, and artists to the festival to show off their projects, and some of them wanted to sell things.
A not-insignificant number of participants who wanted to sell things were just reselling things you could buy at Michaels, or buy online (in bulk) for cheap.
Sometimes with just a little modification, or maybe a creative recombination, or repackaging.
The problem is that you basically have to examine every single item, and then personally decide if it qualifies as art or not.
That's a lot harder than it sounds, and can quickly devolve into a judgemental mess that nobody wants to participate in (we wanted to encourage makers, not subject them to some "must be at least this cool" test, which is scary for people).
Imagine the PR fallout for etsy the first time they tell somebody that their handmade widgets look like mass produced junk.
I think they're in a really tough spot. When they weighed the options, my guess is that they realized that it would be best to let the consumers just decide what they want to buy.