It’s largely a market signal, it seems. I was listening to a podcast with an ex-GM engineer and he said basically the business end is entirely driven by financing vehicles. Very little profit is derived from selling a car itself, nearly all the profit comes from the finance end of the business either on leases or car loans. Americans overall drive cars for a very short period of time before upgrading.
That, coupled with massive consumer preference for “zero maintenance” vehicles like supposedly not having to change transmission fluid for 100k miles. The manufacturers know that such a schedule will guarantee (more) damage, but it’s considered a marketing expense to handle early failures under warranty but sell the idea your car just needs an oil change every 10k miles and nothing else. After that first owner and warranty period the parts are simply considered a consumable.
If you plan on keeping your car for more than 3-5 years, toss the maintenance schedule handbook in the trash and figure out what an actual reasonable schedule is. It’s probably at minimum double the recommendations are.
For my car it’s been message boards with enthusiasts and mechanics who work on my vehicle. Luckily (or not…) mine is a somewhat niche performance car so people tend to nerd out over them.
A lot of it though is ignoring the vendor recommendations for outsourced parts like transmissions - go direct to manufacture and see what they say. This does seem to involve having an “insider” with manuals intended for service techs.
I also imagine fleet vehicle schedules might be informative as well.
Unfortunately I don’t have a very clean direct answer on it - it was a lot of feeling around and when in doubt erring on the side of over maintaining vs under.
Some is simply basic common sense though. We have not developed lubricants that can last over a decade and 120,000 miles in temperature ranges from below zero to hundreds of degrees.
That, coupled with massive consumer preference for “zero maintenance” vehicles like supposedly not having to change transmission fluid for 100k miles. The manufacturers know that such a schedule will guarantee (more) damage, but it’s considered a marketing expense to handle early failures under warranty but sell the idea your car just needs an oil change every 10k miles and nothing else. After that first owner and warranty period the parts are simply considered a consumable.
If you plan on keeping your car for more than 3-5 years, toss the maintenance schedule handbook in the trash and figure out what an actual reasonable schedule is. It’s probably at minimum double the recommendations are.