What if the plentiful number of filler rides which soaks up crowds convinces large crowds to show up to enjoy the lack of crowds which only crowds it?
Transportation experts tell us that if you build more roads, then the roads get used more. What if a successful park is always just successful. And whatever they do to make it more successful, such as ad filler rides, only make it more successful?
Or, look at it this way: in WDW, aside from the MK, the other three parks have a dearth of rides, but, they're often just as crowded as the MK. The MK has lots of filler rides, therefor, it shouldn't be as crowded as the other three parks, and yet, it's the most crowded.
"Increasing capacity" isn't a solution because it causes increased attendance.
A successful park will fill up with crowds to the point that attendance levels off because people don't want to deal with the crowds. More capacity is the same dynamic, just with more numbers.