Why ? This house is old, okay, but not bad for the rhinos. They have rebuild it for them after the last elephant left the zoo in 1983, and now they have four boxes for a pair of two southern black rhinos. The box on the photo was formely the place for three asian elephants....They have amde the ebst what they could do for the rhinos. The hippo exhibit is really bad, the formely zoopdiurector trid to give them away, but the city of Frankfurt, the owner of the zoo, said"No", so the hippos had to stay in the zoo. Now there are plans to build a new own hippohouse in the zoo.
The rhinos are doing very well in the old house, I know the rhino keeper since many years, and I can see that the rhinos are feeling fine. They had bred three times and send the three females back to africa. Unfortunately, two of them died a few years later.
And let me sure you, I know a few rhinos inside and outside exhibits in germany which are really sad and bad for the animals.