Curious.

I find that I do at first and to continue reading I have to be interested. I follow a lot of roleplays that I'm not actually active in. Some of them due to the fact that I have roleplayed with one of the players involved and know that they are a good writer, in that case I normally continue reading the thread due to interest, which is my second reason, if it interests me when I first clicked on it then I continue to read.

A lot of the time I click on threads because I'm bored and I like the sound of the title. Other times it's because when I saw the OOC I didn't think I was up to the standards of the GM's expectations, so just follow it as they develop it.

^^ That's my reason anyway.

PS. My dog. And so are the other to. >:P

Well I follow Roleplays without joining them sometimes. It's mostly just to find some good Roleplayers sometimes, ones that are rather both active and entertaining writers. (See: Few and far between.) While most of the time I just encounter the same bland "died in five posts" Roleplays, there is the occasional good Roleplay that sparks my interest for a few pages.