Because he is the perfect bench/role player for a team, or close to it.
His bat isn’t great, but it’s good enough to be playable above that of a AAAA star at 1B/corner OF.
Also, he can actually play all those positions, and is at least passable (I think, maybe?) at 3rd.
So essentially, you have a useful player who can serve as a backup at four positions, and routinely plays for contracts barely higher than a scrub AAAA guy, which is great for roster construction as well.
So while obviously Hinske doesn’t have magic winner powers that he gives his team, he definitely helps his teams win and is routinely had for a bargain.
Hinske really hasn’t been passable at 3B for a long time, even when he was playing the position in Toronto regularly. Otherwise, I completely agree with you – he’s an excellent bench guy, and useful short-term starter.