Once the MBAs take over there is less incentive provided to staff to innovate and disrupt internal products and services.

The innovators in the company are likely correlated with doing more than 9-5. These people get frustrated that their ideas no longer get traction and leave the company.

Eventually what's left are the people happy to just deliver what their told without much extra thought. These people are probably more likely to just clock in the hours. Any remaining innovators now have another reason to become even more frustrated and leave.