That happens all the time in most Roleplays I been in or GMed myself. I'm unsure why...for myself I know I am real busy doing home works and what not, but I check here regularly, thinking up of my next post. :l 

I get the feeling that to get a group of good, motivated people you need to have a mixture of luck and extraordinary good GM-ing skills to keep people interested. And I mean out of the IC...something I never could achieve with any Roleplays I had. :/