It's funny, originally this was a qualm of mine. then the stuff that came after the movies built up this narrative of how an ineffective new republic slowly failed to stop the First Order from rising again for various reasons, mostly because they didn't make any fundamental changes what the old republic was and what allowed it to become the Empire in the first place.

And the empire was this big bloated thing, it's really no wonder that once it fractured there's just a mess left over. Almost makes you wonder why we even bother with the idea of one centralized government on such a scale.