@Jurek7
Burgers' Zoo is a privat company, owned bij de descendants of Johan Burgers. They are not getting money from the city of Arnhem, which is, btw, not a small town compared with the other Dutch cities.
To build a display like the 'Bush' is not always a matter of money but has also to do with the identity of the zoo. Some zoos are to small, and they don't have the intention to grow much larger, but are focused on keeping their animals in better exhibits or to keep rare species. Other zoos are more focused on keeping their animals in large exhibits, like Emmen, with less species. Zoos like Artis don't have the space for a 'Bush'.
It looks strange but in The Netherlands it seems that the zoos don't have to compete with each other. Every zoo has his own public. Even in a small country like ours you can met people in Emmen who don't visit Rotterdam and vice versa. I spoke a few years ago some people who are living 20 kms from Amsterdam, but always visiting Emmen, 150 kms from their hometown, and who rarely visited Artis!
Rotterdam Zoo could build a 'Bush' but don't feel the need for it. They just build a very large exhibit for polar animals, and an exhibit for savannah animals. This zoo is one of the most visited zoo of The Netherlands, and owned by a foundation.
Another privat owned zoo is Ouwehands' Zoo in Rhenen, not far from Arnhem. How is it possible for this zoo to survive while Burgers' Zoo is in their neighbourhood? This zoo is not very large but attractive to children, with a large indoor playground. The founder, Cornelis Ouwehand, always saw some means to promote his zoo. For example: after Berlin and Paris, he brought the '1000 crocodils' to Rhenen. A famous Dutch tv-series (Zoop) was recorded at a location in the zoo. When the foundation Alertis, who rescues bears, need a place to build a sanctuary, they found it in Ouwehands' Zoo: the Bear Forest.
This zoo has not the money for a 'Bush', but don't need such. Today the zoo is thriving, with a new (privat) owner, with a masterplan for the next 15 years. One of his first things he did was bringing back the elephants to the zoo, building a large polarbear exhibit, and the tiger woods.
Other zoos are more thematic, like Avifauna (birds), Apenheul (monkeys), Dolfinarium (dolphins), Safari Beekse Bergen (safari park), etc.
I hope I have answer your question properly?