Why’s it called a blow job when you’re mostly sucking it?

Because the term started life as "A below job - i.e. below the belt - and mutated to blow job because whispered quickly, in the backseat of a car, that’s what it sounds like.

Honestly, if I lived in NY, this post on it’s own would make me vote for him.

Of course, I’d have to live in the US too, which I don’t, thank some deity.