From what I have read, Rolls Gracie (and maybe Rockson) where not only huge proponents of cross training but also participated in the formation of the Brazilian National Wrestling Federation and their national FS and GR teams.
Then there's Pedro Gama Filho, an early GJJ blackbelt who's family founded Universidade Gama Filho, in Brazil. This institution was largely responsible for Bjj, judo, and wrestling having many opportunities to cross paths.
Obviously the formation of MMA type events was huge. When the early wrestlers did well against BJJ guys many Brazilians knew wrestling was to be taken seriously.
Some time later, after Brazilian Top Team was running strong, American wrestler Darrel Gholar relocated to Brazil to work with BTT on takedowns. His influence was huge.
Another important point would be the mass migration of BJJ'ers to the USA. When the Gracies came to California many AMerican wrestlers and martial artists were then exposed to a whole new art.