@kdfrawg True, but a large part of why it is the way it is that vendors have to do a lot of the necessary work themselves for backporting security fixes and the like. Which, when they've made almost nothing on the handset when sold, is a significant cost to bear, especially later in the handset lifecycle.
It may do nothing for the low-end phones, but for flagships, it means they MIGHT be supported for longer than two years now.