Because of their behavior? Violence was one of the main ways actors resolved conflicts in this period. Didn't like a new tax or that the King appointed his cousin or not your cousin Bishop? Revolt! Have a battle, whoever wins the fight gets his way.

Clovis I the would have absolutely used centralizing tools like railways and the telegraph to enforce his rule more uniformly and ensure his dynasty's success. He only reason why he didn't was because he couldn't.

Dark ages monarchs spent all their time trying to stabilize their regime and enforce their will on the society. We know this because we know how much time they spent marching around their areas putting down revolts and fighting off invasions.