The answer to why it's not a thing is likely the mundane problem of development time.

They have to develop a male and female version already, but having each of those also fitted to the gender they weren't initially designed for doubles(or increases) development time for artists.

It's also going to add to the game's file size as you'll need new models for each - the textures at least could be recycled.

Retro-fitting all the existing gear would be an absolutely massive undertaking and they're likely budgeting dev time to expansions and patching instead. I think the best you'll see is a few popular pieces getting ported over as time allows if the art team is caught up on higher priority work.