This isn't unique to Paradise Vision. It's not uncommon for a girl to come in, shoot enough footage to turn into four or five clips in one sitting, collect her pay, and then go on with her life. It seems like they're "working" lengthy stints in the biz when in reality, they needed some quick cash and then moved on, especially when a producer doesn't release it all at once. I haven't worked with Kim since last year and yet I still have five or six more clips' worth of material that I haven't released yet solely due to backlog.
Even the girls who come back multiple times eventually run the risk of suffering from overexposure, so even if she wants to get tickled for a year solid, it's not feasible to do so because eventually her clips will stop selling and people want someone new.