Control. Hospitals hate having high paid doctors or independently billing doctors. Treating 30 patients can lead to professional collections over 1M. There is no way a hospital or academic center is going to be comfortable paying a doctor that much even if it is justified from an RVU/collections standpoint because they are working hard. That gives the doctor a lot of leverage being a very high producer. They also get squeamish about the optics of the high number and Stark Law, and honestly I think there is a lot of jealously that gets involved when numbers get that high. So the hospital can either just pay the the high income they have earned or they can stick them with the work but cap their pay, which understandably eventually will lead to the doctor becoming unhappy and asking uncomfortable questions about what the production actually is and where the overage is going.
Alternatively, the hospital can pay 2 doctors a very low salary, not have to worry about vacation coverage, and know that if one becomes unhappy and threatens to leave, they can just point and say your colleague is not complaining and say bye.
I cannot tell you how many times I have run into this situation where they are trying to place 2 doctors in a 25 patient practice. It is extremely frustrating. Suggesting that you can handle that load yourself, which you think would be welcome, seems to suggest you are just greedy and don't take your time with patients to do good work.