Oh, advanced 3D CAD certainly makes it possible to design for easy maintenance. However, the effort to do so often isn't made, and often for financial rather than engineering reasons. For cars, the motive is almost certainly financial. It can cost more up front to design a car for easy maintenance. In addition, dealer maintenance is a cash cow, so a car that's easy to maintain could cut into dealer profits. No, I suspect the motives are to make something difficult to maintain outweigh those to make it easy to maintain.

Years ago, I saw a car commercial that touted a particular car's ease of maintenance. It pointed out that over a period of a few years, their car would cost hundreds or even thousands of dollars less to maintain than the competitor's car. I only saw the commercial once. That would've been an ad campaign and concept that I would've love to see catch on like the flu. Instead, I think it was pulled for not being in the manufacturer's and dealers' best interest, and screw the consumers.

Most modern military systems mandate easier maintenance than earlier systems. More parts will be relegaged to depot level maintenance, where the field tech swaps out some circuit boards and those boards get repaired in the rear. Even in jet fighters, things like interchangeable engines and even tail surfaces make both maintenance and logistics simplier.

Back in the early 1990s, I read an article in Airman magazine about how engineers from defense contractors were sent out to airbases around the world to get first hand exposure to field maintenance. There's nothing like having someone work outside on a plane in Minot, North Dakota during the winter to appreciate how hard some tasks are. One thing they learned is how difficult it is to work with safety wire (used to ensure bolts can't loosen) in -40 degree weather, especially when the safety wire is ripping your hands to shreds because you have to take off your gloves to work on the damned things. Like I said, engineers need to get some real world maintenance experience before they're allowed to design anything.