[customkitchen]

That's not a good comparison because it would be even harder to write your own X server. And yet X is still extremely fragmented.

And developing a new compositor also does not require wlroots. Originally there was libweston, wlroots is just another option.

[account42]

It is a good comparison because you don't need to write your own X server to implement your own window manager, which is the part that most people care about.