All somebody has to do is browse the Collaborations board for awhile to see a big difference between what someone like @HazeAmaze is posting and what we're talking about.
One is active on the boards, posts a very specific description of what they're looking for, and is clear about compensation/opportunity.
The others... are treating it like it's a want ad. It's their only post on the Tapas forums or it's a string of posts about looking for unpaid artists. They vaguely post about what they want to do... not what they've done. When questioned about specifics they disappear or want to move conversation to DMs.
And this isn't saying they're all predatory, but as others have stated... Their inexperience leads them to follow bad examples and think this is how good business is done.
On a secondary note, watch when artist seeks writer.
They post samples of art and then we see similarly vague pitches of a Game of Thrones story they'd love them to draw. Where are the 3-4 page pitches that both parties could use to test the waters of how they might work together? Few and far in between.
Yeah, it's a pessimistic viewpoint, but it's born from experience and lessons learned.
Collaborations CAN be great experiences but they can also break you. Choose wisely and with wide open eyes.