There have been Catholic monarchs for ages throughout the Roman Empire, and you cite two edicts from two different monarchs in suppressing insurrection? Your claim is false if you are merely citing two instances and saying that it is “usually” how it pans out.
Also, make note, Dignitatis Humanae is written in context to pluralistic societies being the norm now, but also it was written with the scare of communism very real during Vatican II. The document itself makes the claim that every government is obligated to have public worship to God, it also says that no person has a right to be in error. It merely says that no person should be coerced in joining one faith or another.
It says nothing of Catholic governments having an official religion, and passing laws to protect that religion in that society. As a matter a fact, in these old Catholic kingdoms, heretics were the ones also trying to overthrow the gov’t and establishment, and were punished accordingly.
This was answered on CAL this last Tuesday. The first caller for Tim Staples asked this very question. Tim answers very well. His point is that no person can generally be coerced into and out of the faith, yet that doesn’t necessarily mean officially Catholic governments cannot protect their own society and traditions.
So, generally, these Catholic monarchies were right to try to suppress heresy and maintain the status quo.