Ease of maintenance is not really a priority of engineers, and maybe never has been. It's just that for the first few decades everything was mechanically simple and was not being fitted into as small a space as possible. "Efficient" to an engineer does not refer to maintenance. I was appalled how complicated relatively simple jobs - replace a water pump, thermostat, starter, fuel filter, etc - evolved to be merely in the couple of decades from 1970 to 1990.
Some good design principles for military softskin fleets are simple to operate, simple to maintain, and approximately disposable after a few months' wartime service.