Patches are often applied late because it's not rare to experience serious disruption. Anyway the software being patched is poorly made in the first place. The problems caused by patches are actually another sign of very poor software design.
And not the least: after 25 years of development on Windows the patching mechanism still is in a sad state, requiring unreasonable time and resources to find and install required patches. It is very clear that quality isn't a priority for Microsoft *at all*. They only care about making money, what happens to their customers and how much time they waste on using and maintaining their products does not matter to them as long as they keep buying.
Rob