I'm just gonna copy and paste a response to another similar comment:

The point that I am making (obviously, I think) is that tradeoffs exist, even if you don't think the right decision was made, your full view into the trade space is likely incomplete, or prioritizes something different than the engineers.

Putting some random number of hypothetical mpg improvement was clearly a mistake, but I assumed people here would be able to get the point I was trying to make, instead of getting riled up about the relationship (or lack thereof) of oil filters and fuel efficiency.

I'm using this hypothetical to illustrate the point that: tradeoffs exist, and that you (we) may not have full insight into the full complexity of the trade space that the engineers were working with.

Putting some random number of hypothetical mpg improvement was clearly a mistake, but I assumed people here would be able to get the point I was trying to make, instead of getting riled up about the relationship (or lack thereof) of oil filters and fuel efficiency.

Glad to know in this hypothetical car scenario the owner decided to not get an oil change leading to the total loss of the vehicle. That seems very realistic and definitely something that car designs should be optimized around.

Or, we consider that 2mpg across 100,000 cars can save 3,500,000 gallons of gas being burned for the average American driving ~12k miles per year. And maybe things aren't so black and white. You're argument, in this hypothetical, is that negligent car owner who destroys their car because they're choosing to not change the oil is worth burning an extra 3.5millon gallons of gasoline.

Right but what I'm getting at is that there can be tradeoffs that might make designing for maintainability mean optimizing for something less important to the end user.

Do you optimize an engine for how easy it is to replace a filter once or twice a year (most likely done by someone the average car-owner is already paying to change their oil for them), or do you optimize it for getting better gas mileage over every single mile the car is driven?

We're talking about a hypothetical car and neither of us (I assume) design engines like this, I'm just trying to illustrate a point about tradeoffs existing. To your own point of efficiency being a trade with durability, that's not in a vacuum. If a part is in a different location with a different loading environment, it can be more/less durable (material changes leading to efficiency differences), more/less likely to break (maybe you service the hard-to-service part half as often when it's in a harder to service spot), etc.