>>512868662
(Part 1)
It really is just corruption. However, obviously this answer by itself is too simple, so some context must be added. Spain was worried about their colonies rebelling because they were so far away and did not sufficiently settle them with whites who would culturally assimilate vast swaths of land quickly enough, so they had to keep them intentionally divided, isolated, and hyper-dependent. No direct communication or trade with other colonies, only through Spain. Too many minor decisions necessary to maintain stability in, as well as improve colonies and the living standards of their subjects had to be approved by disconnected higher authorities first. It became obvious overtime even to those of positions of privilege and power that this was unnecessary, so they naturally felt they could go it alone, but they couldn’t, because the colonial system was designed to make them incompetent. They gained independence, and even though the upper class were resentful towards Spain, there was still a significant degree of disconnect from the general populace, and this was seen in the codified inequality inherent in the system, from white aristocracy ruling over a brown masses, to the encomienda system which was just reformed from the plantation slavery of natives, now with a small amount of dirt pay. Wherever power was concentrated is the part that mattered most, and obviously that was Mexico proper, that being modern-day Central Mexico, basically CDMX/Estado de MX, and all surrounding states roughly corresponding to the Reino de Mexico in the larger Virreinato de Nueva Espana, as pictured here.