Where did you come up with the $2-3000 number?
Your second point makes no sense to me. People actively seek out cruising, ships stop at ports and passengers spend money on the local economy, you are not captive at a land based resort.
If it is in a land based resorts best interest to be all inclusive why wouldn't it be in the cruise lines interest to be all inclusive.
The reason resorts went to all inclusive was to provide a hassle free experience for their customers. It's huge selling point for that industry.