Because it's not what you care about. What you care about is immaterial. It's what your estates care about.
If you move in and suddenly dispossess the local nobility, your own nobility will watch that happen and be like, "wow, our king totally doesn't respect the rights of his noble subjects" and get mad. If you move in and dispossess the local clergy, your own clergy will watch that happen and be like, "wow, our king totally doesn't respect the rights of the Church" and get mad.
If you move in and suddenly dispossess the local burghers, your own burghers will watch that happen and be like, "wow, our king totally doesn't respect the rights and charters of the cities."
Social class was traditionally a much stronger motivation than nationalism, you know.