Unless there is some damage there is nothing (that I can remember) to stop it from coming out. The prop shaft slips into this adjustable bushing / bearing. It could be just suction keeping the shaft from coming out. Take the bushing out and see what happens. Looking at the drive shaft again I don’t think its necessary to remove the key to get the drive shaft out. Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.