Adding on to the other (very good) answers here, a large part of the point of Dune is that the political environment at the beginning of the books is utterly stagnant and forcibly kept that way by dozens of power brokers who don't want change for any reason. Between the Bene Gesserit's machinations over the course of centuries, the Spacing Guild's monopoly of travel, CHOAM dominating all economic trade, and the Emperor and the Major Houses shoving one another back and forth politically over eons any potential new players would simply be obliterated unless they operated as just another House playing by the same rules as everyone else. The Great Convention ruthlessly enforced stringent feudalist terms while heavily restricting any potential avenues for disruption (most notably the use of atomics or thinking machines) and was enforced by every major power player simultaneously, on threat of utter annihilation.

It took having the Bene Gesserit's main long-term goal of producing the Kwisatz Haderach happen without their knowledge on pure accident combined with said legendary figure uniting the entire Fremen nation behind him, catching the Emperor and Great Houses completely by surprise in one of the most one-sided battles in history, and him discovering the full lifecycle of the worms that make Spice while also giving him unprecedented control over said process (and the ability to destroy it outright) to shatter this equilibrium, and then it took his son spending nearly 4,000 years dismantling these power structures and setting up the Golden Path to allow humanity the ability to scatter and evolve once more.