Manspreading is not because of the private parts or anything like that, it is that men have a tendency to ‘fill the space’ they are in, I haven’t figured out if it is cultural or instinct. There are some women who do that, but it is rare, because women tend to shrink themselves into a space IME (women on the other hand do other impolite things, on trains and buses they put their bags on the seat next to themselves, and then when someone indicates they want to sit there, give the person dirty looks and make it obvious they aren’t happy; these are rush hour service, when the trains and buses fill up, but they seem to think they have the right to use their bags to 'maintain their space").
As far as planes go it is going to get worse, to fit even more seats in, aircraft may have even narrower seats so they can fit in an extra seat in each row.