boats with that style hull sitting on the keel in boat yards with the hull deflected considerably. The French are into very light hulls and that design makes for easy constriction. That deflection means the fiberglass strands are being stressed in a way they were not meant to be. After a few haulout-launch cycles the glass is pulp. An accident waiting to happen.

Sure you could run a strut through the keel up to the cabin top. Many ultralight racers are built that way. But, pleasure boats have to appeal to buyers that don't want structural members in the middle of their living space.

As Jon said you wouldn't step an unstayed mast on deck but the same issue is true with stayed rigs. Keel stepped is so much stronger and more reliable. Would a deck stepped mast survive a forestay snapping - I doubt it.

I had a forestay chainplate break due to metal fatigue while beating into 20 knots. The rig shuddered but stayed put. Yes it had a babystay, attached about a third of the way up that helped but I believe if it was deck stepped it would have come down.