[quote]It drives me insane that there are seemingly dozens of people on the site that simply float around and state interest in RPs without ever joining any[/quote]

From my personal experience - and I don't really do the described activity often, I'm just playing Devil's Advocate and trying to think of a reason why someone might do this - I've stated my interest early on in an Int Check based on the concept, and then a bunch of new ideas have been added to the RP, and it's ended up with me doing a 180 with my interest in the RP, and not wanting to participate. That's happened a couple of times with me. 
That said though, you'd have to be remarkably picky to do that in dozens of RP's one after the other, and I know it's not the case that [b]every[/b] int check goes like that. But might explain some at least? IDK.