You missed my point. Of course people go into Disney's Animal Kingdom. The problem is if you compare pre-DAK to post-DAK, the opening of the 4th park didn't cause guests to extend their stays by any substantial degree. Instead all they did was shift their schedules. Instead of spending 3 days (out of 7) at the Magic Kingdom, your typical family may have switched to 2 days at MK and 1 at Animal Kingdom.
Problem is that doesn't make any more money for Disney to justify the extra gate. Put it this way: If Disney opens a 5th park, their operating expenses grow by about 25%. They need more ride toll booth attendants, security, Guest Relations, ride attendants, restaurant staff, gift shop clerks, and so on. They also need to pay for utilities, maintenance, landscaping and all other expenses associated with running a multi-billion dollar park.
So Disney's expenditures grow about about 1/4. How would they cover that added expense? Can you honestly say that if Disney opened a 5th park, you would increase your own personal spending by 25% with every single trip you take?
Very few people would do that. As I illustrated, most people would just keep spending the same amount of money, while shifting their park schedules. They'll reduce their time at MK, Epcot, DHS and DAK to squeeze in a day or two at the 5th park. They'll skip the Epcot t-shirt and buy a 5th park shirt.
End result is Disney's spending millions to run a park without any real prospect of added revenues covering added expenses.