why do ALL B series VTEC trannies come with such short gearing?

Because, when you have a motor (such as a VTEC motor), with a broad powerband...you can afford the shorter gearing. Longer gears are generally best matched to a motor with a peaky powerband to keep you there longer. If you are making power everywhere, you don't need the longer gears and can better make use of the shorter gears to pick up speed much faster.