Solar panels are expensive, and for the sailing that 98% of sailors do, are not that useful. (see the layout thread). 98% of sailors spend weekends cruising from anchorages/marinas/docks etc. and do a 2 week vacation. They don't really need solar panels because they are usually using the engine enough to charge the batteries. So manufacturers don't supply them or have a place to fit them.
what about the people that live on their boat? wind generators are nice but most of them are loud and expensive.