Interesting... Usually, there aren't a lot of sims when a community lot is first loaded, but more come to the lot over time. If the lot is owned by a sim, the cause is rooted in the business rank (the one that depends on customer loyality) in Open for Business. There may be less sims at night. If you bring children with your sims, you may see children on the community lot (same with pets). I really don't know what else to say.
The Apartment Life lot rating is lot class and it shouldn't affect how much sims visit it. It affects which social class visits it more (you'll see a lot of socialites on high and a lot of jocks in middle class). Each of them have their own story to tell and their own gesture they use. These are the sims who live in apartment units not rented by your sims.
More about social class townies in this The Sims Wiki page.
