Why do we stand for possibly the poorest service imaginable
Because if you are "small fry" you don't really stand a chance.
Fleet operators (large civil operators and the military) receive the manufacturer's highest priority wherein parts and technical support are factored into the operator's ongoing operations.
For single users or those with small fleets, well, they hardly register on the manufacturer's radar so to speak.
Producing spare parts and keeping them in stock just isn't defendable in the eyes of the manufacturer's financial controllers for while it may have longterm unwanted consequences you are still only talking about losing the odd customer and not a fleet operator and what's more, if all the manufacturers club together so that their lack of commitment to individual and small operators is the same, well - hey presto - you don't have anywhere left to go.
The world of the 21st century is about control, control by government and control by large organisations. Consumers will increasingly become "plebs" to be tolerated - and we will have no choice but to accept it.
I could be wrong - but I doubt it.