It's a phrase that has a specific meaning in business. It describes when a manager (or group of managers) make decisions that protect or improve their personal position instead of thinking about what is best for the company and/or shareholders.

"Entrenched" has a literal military meaning. It means "in a trench." A trench is a long groove dug in the earth, maybe 2 meters wide and 3 meters deep, maybe miles long. In World War I, soldiers dug trenches in the earth. Soldiers above ground are easily attacked. When they are "dug in" and "entrenched" they are protected against attack from guns, artillery, and even explosives. Once soldiers are "entrenched" it is difficult for the enemy to get them out. Figuratively, a group of leaders in an organization are "entrenched" when their positions are secure. There is no chance of removing them. They have been there a long time. And it is difficult to get them to do something new.