It is a classic engineering conundrum. Increasing the size of a hatch directly impacts construction cost, structural integrity, and reliability -- to say nothing of decreasing the ease and speed of operation. Ask any Navy sailor or Marine what it is like to open one of these:
Granted, there are faster acting clamping mechanisms, but they more failure prone, heavy, and many times more expensive. Egress has been a major concern on combat ships since iron hulls were introduced so it is an excellent place to look for relevant data. The
BIG difference here is general boating can't depend on the level of training or physical fitness that the military can.
Please don't take any my comments as "this is the best we can do", because it never will be. I am only trying to point out some of the practical constraints and give people a sense of the great number of person-hours at sea where existing standards have proven satisfactory.