For example, once you accept the existence, or at least the need to discuss transgender people, then the term "cisgender" or something like it naturally arises as a means of distinguishing people whose gender identity and sex match from those who don't without being offensive. You could stick with "real" or "normal" if you like, and see how far that gets you in a face-to-face discussion without being slapped.
Then the "third-wave feminism" etc emerges because, you know, feminism like everything else goes in phases. It is, as I say, something of an oversimplification, but loosely speaking:
"first-wave" = voting rights, property rights, legal issues etc.
"second-wave" = a broader search for equality, eg equal pay and equal family rights and roles, etc.
"third-wave" = pretty much everything since then, sort of.
But if you'd ever actually read into all this then you'd know that already.