Actually, about one-half of the hotels and condotels on the island now do have pools, and a number that don't are adding them. I personally think it won't be long before it will be a necessity for any hotel on the island above the budget level to have a pool:
Here's a list of hotels (may have missed a couple) with pools, listed roughly from north to south:
Playa Blanca, Avalon, SunDiver, Journey's End, Essene Way, Captain Morgan's, White Sands Cove, El Pescador, Belizean Shores, Seven Seas, Blue Tang Inn, Paradise Villas, AquaMarina Suites, SunBreeze, The Palms, Ramon's Village, Belize Yacht Club, Hideaway, Exotic Caye, Xanadu, Villas at Banyan Bay, Tropica, Banana Beach (two pools), Mata Rocks, Royal Palm Villas, Victoria House, Caribe Island Resort and Sunset Beach. Also, nearby: Cayo Espanto (individual splash pools) and Caye Chapel Golf Resort. At present, no hotel on Caye Caulker has a pool.