Loss of efficiency due to prop angle

Question? why do most boat builders still use the method of pitching the motor a few degrees and running a straight shaft with the prop pitched a few degrees losing some efficiency because its not perpendicular to the hull ?????

By using a constant velocity joint so the prop could be mounted 90 degrees or what ever angle that gives the best efficiency?????

Is there a reason I,m unaware of????? ,as marine constant velocity joints are already in use on surface drives !!!!!!!!

Talk about slow to change old ways of Thinking ! While above water what you can see has the coolest ,newest designs !!!!!