Coming at this from the perspective of a sailor I think you're ignoring one major aspect - how difficult it would be to build a stable, strong catamaran with the techniques and materials available at that time, that would be capable of carrying as much as a fluyt or Galleon.

They surely encountered other peoples who had developed the much more stable boat design, and would have had significantly more room for equipment, provisions, crew quarters, and cargo in addition to the ability to cope with rough seas much better.

I think that there are some assumptions in there that may hold at least part of the answer for you. If your assumptions are correct why are catamarans still so rare in military and cargo shipping even though we now have the materials technology to build large catamarans? You may also want to ask why other non-European cultures did not make more use of large catamarans in the past?