Not exactly a theory around the story, but more a theory around a location in the Pizzaplex. Kid's Cove (the only Foxy themed area) just seems to exist without its own Foxy to add to the Pizzaplex, it's just one of those non-story related areas like the Glamrock Beauty Salon and Chica's Bakery.
Before I get into it, doesn't anyone feel like the Kid's Cove is supposed to be another daycare area? Now regarding new or old, that's the question; how long has the Kid's Cove area been around for? This is probably something pointless to think about, but I feel like every area in the Pizzaplex has a story to tell if you look around and notice anything.
New:
It was built to replace the Daycare Attendant's space after too many complaints off customers, like the one involving the little kid who gets upset now whenever the lights in his room are on or off. Kids are scared of Sun & Moon, so FazEnt builds a new Foxy area but they never got around to bringing in a Foxy.
Old:
The place was set up, but they put the money into the Daycare Attendant instead.
The more likely answer:
The company just never got around to bringing in a Foxy yet and that's about it.