Its been touched on, but as easily as I can explain it:
Its much easier to tend your shop when your present and active there every day.
The family that owns 1 park, and sees success, is likely successful because they are there every day, they live in the community that the park serves, they have a solid feel for what their customers like and want. They see small problems and nip them in the bud before they become large problems. They have a close relationship with the people they hire, know their families, know their struggles and dreams, know what they're good and and where they struggle.
The family that owns 2 parks, often seperated by a large distance can't be in the all parks every day or even week/month, therefor they have to hire people to manage these ventures for them. Small problems creep up and are overlooked until they become big problems, its significanly tougher to understand the markets they serve, they're not as familar with their employees, it becomes tougher to retain them, its harder to put them in position to succeed.