If Lebanon is really under "Iranian occupation"(I know it's not) then why do we have a US embassy in the first place?

Seriously I don't get,how is Lebanon under "Iranian occupation" and we have a US embassy,not only that but the US embassy in Lebanon is really huge,we could built a lot of stuff in its place,after all,if Hezbollah really ruled Lebanon,you'd expect them to be the only decision makers,no? I don't get.