Mexico traded monarchy for dictatorship; it certainly wasn’t democracy they were pursuing. Texas left the Union in relatively short time; apparently they realized their mistake.
My wife is a Spaniard (Gallega); they want Gibraltar back as we want the north of our island. Some Scots were willing partners of the English (even participating in the Protestant occupation of northern Ireland); three hundred years later it looks like almost half of them have had enough...
From all I’ve read about the way Spain governed-and taxed- its territories in the new world in the 19th century, I’m guessing that just about anything was preferable to that-at least in the short term, and especially if you were not-exactly-rich mestizo ranchers, like my antecedents were.
The Basques have always been a revolutionary bunch, too from what I’ve been told, including the ones who came to the new world-prices on their heads in Spain and all that-and lot of them still want to be independent of Spain, too-when I was in college, the separatists over there had one of their uprisings, and one of my friends who was a Basque with family in Spain packed up and took off for the airport, telling us all he was going to Spain to fight with the Basque separatists-we all thought he was totally nuts-but he was back the next semester, raving about how good it had felt to go there and be a part of the push for independence.