If they did that, Israel would actually have to play by the rules. Being directly controlled by the US government would mean that they wouldn't be special anymore.

"If Israel didn't exist we'd have to invent it to protect our interests in the region"

-Joe "the bloodthirster" Biden

Israel will never be an official US territory for the same reason that Guantánamo Bay never will be, even though Israel is more important to US interests than all but a few states