Luxury car buyers don't want to maintain their cars. They are ok with paying someone else to do it, and cars come with long warranties these days anyway. Many choose to lease rather than buy, because that way they will always be driving a relatively new car.

These people are getting exactly what they want from the luxury cars that are currently available. If a manufacturer spent money on making its luxury cars more durable and easier to maintain, they would need to raise prices and would then lose sales to other brands.

In other words, this situation is a result of consumer preferences, not a conspiracy by manufacturers to cut quality. And that applies to a lot of things, not just cars.