Not dealing in specifics but general terms.
Many of the parts used on cars and trucks are not made by the car manufacturer, they are supplied by specialists. Airstream doesn't make tires, axles, appliances etc. Same thing at the car manufacturers.
For cars and trucks there is an entire industry, collectively known as the Automotive Aftermarket that fills the shelves of automotive parts retailers. Its a massive industry. There are many parts that are single source but if the car population merits the expense of tooling and R&D somebody out there is offering it in a lot of situations, especially wear and tear items.
This Aftermarket industry has been my employer for 36 years.
2005 Dodge Ram 2500 5.9L 6 Speed
16" Michelins, Hi Spec Wheels, Max Brake, Carslile Actuator, Equal-i-zer, Dill TPMS. Campfire cook.