That overstates the difference as mergers hardly destroy the old companies in their entirety.

Instead it’s the same kind of shakeups you regularly see in government agencies. Picking one small example, HERSA is a merger of the Health Services Administration (1973–1982) and Health Resources Administration (1973–1982). However currently one of its major functions is managing the Ryan White HIV/AIDS Program that showed up in 1990.

There is a LOT more personnel churn in private sector than federal government.

A merger frequently involves major shakeups in both the acquirer and the acquired. You don’t have to, and shouldn’t destroy the old companies. You just want their resources redirected to more efficient uses every so often.