I like the idea Hook’s coming from SB on the magic ship, and some reverse curse thing already happened.
I don’t think for a second Hook would willingly work for WWW as Hook’s goal is to get Emma to love him. He can’t do that with tricks or magic, so I don’t see him partnering up as he did with Cora. Revenge is a different thing than love, and he has expressed a desire to be more honorable and circumspect to really impress Emma.
The WWW could trick Hook though, make him think she’s just a concerned ….someone…who is “invested in their future” (pull a page from Rumple’s book maybe?) and say she wants to help Hook find Emma, that if he doesn’t, her family would be in trouble (to make sure he feels some urgency to it so as not to question her story), and that he has to bring Emma somewhere. Then (Admiral Ackbar voice…) IT’S A TRAP….but it’s not like Hook knew about it.
As for why not anyone else, well, there could be lots of reasons. We just don’t have enough context to do more than wild guesses at a dart board. (Graham can throw mine).
“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass