a lot of times I see people say tumblr is a bad place full of SJWs, creeps, and just general annoyances.
Why are tumblr posts still made in spite of this?

Because Tumblr posts get likes.

So are people so shallow that they hate tumblr but expose the people on tumblr to get likes? That's gross.

The world is a gross place, my potassium-rich friend.

People are unwilling to compromise that their are parts and sections to every website. You've got people who hate certain things and love other content on the same site. Ergo the generalization of a lazy mind.

Because it's easy to just screenshot what's on your dashboard

Tumblr is used for bullshit. Doesn't mean it can't be funny. Like 4chan. Shitty people(most of the time) but can be really fuckin funny