Like a lot of things Tumblr was at some point one of those off-the-beaten-path fringe social media sites. From the 2009-2012s I remember it being mostly alternative culture like piercings, tattoos, dyed hair, emo/scene/hardcore/alt fashion etc, But at some point the whole site flipped as it got popular. It all depended on which corner of it you resided and which blogs you followed. Then all the high culture/fashion blogs/influencers etc started to emerge.
But yes, if you think about it, at that time in its height, porn and nudes could be cultivated into a couple of categories:
-Mainstream porn with actual pornstars
-Cam girls like livejasmin(lol) and myfreecams
-Amateur nudes on social media sites
-Maybe also the most amateurish and anonymous would be 4chan girls and reddit gonewild.
So back then girls literally did just get naked "for fun" and it was awesome. Girls you could literally befriend and get nudes off purely for yourself even if they never got naked intentionally was also a perk. There was just a big kink about linking with people you'd never meet, getting naked, and jerking off to each other. But it was only a matter of time before girls realised they could make stacks of cash from faceless anonymous people who weren't exactly good looking but would pay to see a hot girl naked. It started on tumblr with premium snapchats, then Onlyfans was created. The rest is history unfortunately. It'll never go back to that as it will only take a girl not long at all to realise why is it that she's doing this for free when she could be making money out of it?