Also, most languages have no such distinction. For example in my native language Hungarian we either use the English word "gender" or say (the equivalent of) "social sex" and "biological sex".
It's a niche thing. I understand that some people feel sensitive about sex/gender or the differences between transsexual/transgender/transvestite/queer/crossdresser/drag-queen etc. But for the vast majority of the people this just isn't a topic of interest.