You can't make women do things they don't want to. It'd be great if all women secretly wanted super long thick hair and the encouragement of some guy was all it took to get them going, but they don't and that's OK.
The ones that do want it and have the time and the right genes to grow it are the rare special ones, at least from a physical perspective. Of course there's more to that to women though, and they can be amazing in a thousand different ways.
For the rapunzels out there who do exist, their rarity and dedication makes them seem more special and more lovely than they would be if all women had hair to the floor. I kind of like that, even though it'd be nice to see more of them.
Just my two cents.