First it had to be small enough fit in the garage.
Second, it had to be big enough to fit my family of 5 plus all of our gear for a week of camping out on Lake Mohave.
Third, it had to be quick enough to pull by 250 lb ass out of the water on a single slalom ski.
Fourth, it had be small enough that it did not throw a wake so huge that would scare the kids when they were learning to ski.
All of those requirements kind of dictated a 21' boat.