@tessw I have also been thinking about this a lot. The things that take off on Tumblr vs Instagram for me are both wildly different, and usually the dumbest/silliest/most mindless pieces. I think, honestly, the general public on social media really only wants soemthing that's easy to consume and spread. So if they have to look at a piece too long, they're less likely to enjoy it and pass it along! MADNESS.
But I like to think of my Tumblr and Instagram audiences as a completely different group of people than art directors and publishers, who usually want depth and complexity. Social media is for junk food art- sketches, doodles, fun and fast and simple. If someone likes your stuff, they'll then go find your portfolio and enjoy the more advanced stuff.
Anyways, that's been my interpretation so far. I think Lee and Jake have both touched on this during some videos, too.