As someone who posts in Casual largely:

A) A day between posts isn't anything to get worried over. Sometimes, it can be a week between posts. Slow and not ideal, but not dead. If the OOC is semi-active, though, it's usually not a problem.
B) Since I signed up, I've been in at minimum 17 group rps. They're all pretty much dead now. It's a problem with group, the GM can get bored or pulled away by life, and if one person leaves, it can halt an rp entirely even if they weren't the GM, depending on what their character was doing.
C) Depending on how long a post should be, they may not be online long enough to actually respond properly, or they may have more inspiration for another rp and focus their writing there.

So personally I don't think it's a problem with just 'Free'. That aside, the mods have confirmed that it's up to GM discretion as to where your rp is and if you want to take a stab in the Casual section for a more reliable group, go ahead.