Yes, I'm sure most people on this website have ran into seemingly bad design choices which made sense once they knew more context. But that doesn't mean that all bad design choices are like this.
Specifically dumb oil filter placement is an example of such a case where the _only_ legitimate justification is design cost saving for the manufacturer (re-using an existing design meant for a different car).
You can maybe argue that saving on design costs (and I guess also re-tooling costs) is a saving that gets passed onto the consumer. But that consumer is unlikely to feel like they're saving much money when cars depreciate faster than ice cubes in the desert, and when their oil change is 2+ times more expensive every 6 months. Really that cost savings will only really benefit the manufacturer (well, at least until they tarnish their reputation).