Stability should be difficult to maintain and unless you give your estates powerful privileges and expand somewhat slowly then you shouldn't expect to have positive stability.
This will make radical reform a longer (and more realistic) process as you can't just eat all the stability hits and survive. You need to carefully maneuver so you are able to stay in power while reforming laws and privileges or face fierce resistance and potential disasters. This also makes you more hesitant to reform and aggressively conquer as it could destabilize your nation which makes it harder and harder to maintain stability (since your losing the stability gain from privileges plus the loss from reforming as well as all of the low control provinces lowering stability) and cause you to spiral. This encourages more cautious play instead of the reform happy affair games like Victoria 3 encourages.
