Honestly, sometimes I make sign-ups for the sake of making them or on a whim. It's not always indicative of whether I'm genuinely "invested," more "let me get a post or two in with this funny ass concept before this thing tanks" lmfaoo
So -- I'll actually answer your other question about post frequency here, Ice -- it's up to the sociability of the GM and the other players to keep me around for the long run. Otherwise, if there's no real conversation or sense that the GM really cares about their player base, there's nothing to gain from my perspective. On the other hand, great OOC experiences breed consistent posts from me. Not that I don't have other hobbies, but I really like dedicating time to a roleplay I care about, and the people that keep it afloat are a big reason for why I care.
I think I could be a decently sociable GM but it all comes down to motivation. I have a plethora of ideas but lack the passion to write for them. That's why I haven't started a roleplay yet, although I'd like to.