I suspect if women went braless since the begining of time. Crossdressers would have to invent bras just to hold breast forms in place.
Even my first experiences in crossdressing as a kid I had to load the bra with something; nylons, panties, socks. An empty bra seems only to to beckon being filled. Seems the bra was only the means to obtain breasts. Now days it is silicone breast forms, so much better than socks. But I think it was the breasts I wanted more than the bra.