Rare 14 lb Bowling Balls

I don't pretend to understand why these 14 pound bowling balls are rare or why they sell so well, so I'm hoping someone will tell me. The first item's description reads as follows:

Columbia Game Pearl Hard to find Great for drier lanes The GameTM Pearl is a great looking complement to the original Game which was designed for heavy oil. Game Pearl is designed to get down the lane easier and make a strong, continuous arcing backend motion. The extra length comes from the pearlized shell which has a lighter loading of the TEC2TM particles. Game Pearl has a low Rg core (2.480) and high differential Rg (.051) for 5-6 inches of flare.Specifications are as follows:Coverstock: TEC2Color: Red/Blue Multi-Pearl with Silver Sparkle engravingHardness: 75-78Factory Finish: PolishedHook Rating: 22