SDDM will keep working, and KDE maintains a LightDM greeter. You don't even need to use a login manager, most people in the BSD space launch it from the tty
I mean, if that's the way they like it, that's fine. It feels a bit quaint, though, at least to me. If a graphical desktop is what I want anyway, why not make it automatic? I'm not judging, just trying to understand.
Not what I'd choose, but I think that is the beauty of the whole free software movement - one thing you get in utter abundance is choice.