I agree you have to research your scenery before you book, but with a week to explore a destination you can do all the excursions instead of just one. You get bored with the scenery? go to a sister property to try thier resturants, bars, pools, and beach.
Some ports i dont even want to get off the ship and after a while even on a big ship stuff can get boring and what choice do you have besides going back to your mini sized room or taking a long swim.
The main advantage is for the bargain traveler. while high end resorts compare with the more expensive cruises fairly well the bargain shopper will find more bang for the buck at an all inclusive.
Case in point...I am looking at a bermuda cruise out of fla for 7 nights at $299 (great bargain right?) not so add $100 taxes, $500 airfare, $100 hotel to stay an extra day to get a flight at $500 instead of $600, $100 for transfers, $150 for tips (taxi-porter-ship people) and that brings the total to $1550... then add a bar bill with 15% added to it, for 2 adults, for a week, and you can see that it is not a bargain. Compared to 7 nights AI cancun
for $1650 with everthing included...no math required...and no bar tab when you check out.
It's a lot cheaper to visit bermuda on a ship than a resort but mexico has tons of AI resorts which can be tried cheaper than a cruise. I guess you have to try both to appreciate what great vacation options they both are.