That wasn't his job. His job was to conquer, it was the "missionaries and Inquisitorial teams that followed those conquests that were supposed to do the job of turning those planets into loyal parts of the imperium.
Same for the Primarchs, they conquered, but for the most part it was the Imperial Army and the Orators who's job it was to maintain those conquests.
Surely it is the duty of a conqueror to hold the worlds he takes? Otherwise he's just a raider with pretensions of greatness. It isn't solely the province of others to make the world loyal, how the conqueror goes about taking the world has an overwhelming impact on how the world feels about becoming Imperial. It determines how open they are to the work of the missionaries. The worlds taken by the Primarchs for the most part were willing to listen to the iterators, because of the strategies used to take those worlds. The worlds Macharius took uniformly rejected Imperial rule, clearly that reflects badly on how he took them.
"Look into my eyes, and see your death."
"Let them hate, so long as they fear."