I think it's because they keep sinking commercial ships and firing missiles at Israel, no? They also shot missiles at Russian, Chinese, European, Panamanian, Japanese, Korean, and South American ships.
Why were bombing them now is because Trump's a dumbass and needs to distract everyone.
No, the waterways the Houthi are murdering sailors in are used primarily to transit goods between Asia and the rest of the world. The Houthi aren't targeting anything other than innocent sailors.