On the centralization of power: you also end up in a situation in society where with so much power invested in so small a group it can become easy to throw it all down on the ground. You end up with hilariously few supporting pillars of government and at any moment or staunch disagreement with policy one of those pillars can move to the side and send the whole system crashing down so that it may step up and assume the position of power out of alliance with the other few pillars and agree the last guy was a shit-head, or a general apathy or fear.

This feeds in a way into banana republics and presidential dictatorships where so much of the power is invested in the strong man with a parliament running a thinly veiled attempt to look democratic. The president has to carefully balance the interests of his few supports to keep in power so one or all don't over-throw him. This is how coups work, one - namely the military - gets fed up and lets new leadership take over in a military coup.

Failing that, you put morons in power in the offices below you and lead by looking like the smartest guy, and you just made so many careers in the right places they'll lick the bottom of your boots forever. The people meanwhile; disenfranchised, otherwise poor, without a voice, and presumably without a vote can't do anything to stop you.

Once you decentralize government or make more offices to help keep the then-ruling party in place the less likely it's all to come undone when someone gets mad at you. If one office throws a shit-fit so what, at the end of the day the nation continues to plod along as a mild annoyance fumes and sputters into the background until it gives up or is fired and replaced by someone more skillful and or thankful.

And in the environments that these highly centralized, dictatorial governments arise in are environments where the economy may not have much in the way of diversity. There's going to be that one major resource the powers that be hang over heads or use to get the capital to hold power while everyone else meeks out a substance living farming.

Based on my understanding of the German economy at the time of Hitler's rise there wasn't much left of an economy for the common people to use. Hitler came around promising to make things great, did that, but then the government held all the resources they acquired or reacquired for Germany among themselves thereby monopolizing power while the German people got none or little so they would keep in line and not revolt against the State. Or if they did the much better financed and supplied SS would go in and kill them all.

You could probably argue something similar with Stalin, or that his staying in power relied on the centralization of Russian heavy industry in the state and the entire centralization of the Soviet economy so that the government ruled it all, and not collectivist communes across the country capable of practicing their own socialist economy to better make their community something to seriously consider by the government. Trotsky couldn't survive when Stalin wrapped everything up under his great coat.