Because with Android's update process you cannot opt to push anything but the latest update which is always an unproven by its nature.
It isn't like Windows where you can opt out of the latest service pack for a while and wait to see if it is stable. With Android you either take the latest update or you don't.
You can install updates via downloading the updating and flashing. This isn't too difficult (basically what you have to do if you run a ROM). It's often how people opt-in to updates that are rolling OTA before their device wins the OTA lottery.
Because with Android's update process you cannot opt to push anything but the latest update which is always an unproven by its nature.
It isn't like Windows where you can opt out of the latest service pack for a while and wait to see if it is stable. With Android you either take the latest update or you don't.