That's the thing, I see new cars getting more and more expensive, but the cost of maintenance for existing cars hasn't really gone up significantly. It just seems like folks stopped doing it, or in some of the cases where I've actually interacted with folks, didn't even know it needed to be done. I feel like the average American does not know /anything/ about cars, how they work, or how they need to be cared for, and either simply take it to a dealership (most expensive option) or assume it'll be fine forever and do nothing.
I religiously maintain my vehicles, and I do it myself, and that is not something that comes out of privilege, it comes out of a rural blue-collar upbringing where people did this /for economic reasons/ because we could not afford to take a car to a mechanic or dealership. The price of 6 quarts of oil has not materially changed in the last 5 years, even though everything else has increased in price significantly. The cost of tires hasn't significantly changed in the last 5 years. Tires /are/ expensive, especially good tires, but it's always been so and any set of tires should last 4-5 years under normal driving conditions (tires age out after 5 years, regardless of tread depth). If anything, tires have gotten massively better, so while their price is still high and not going down, you get much more value for money today than 10 or 20 years ago.
When I see 90s era Japanese cars still on the road, /these are the easiest and cheapest to maintain/, which means that the folks who own them should be able to keep up with maintenance no problem. Even newer (but still old) Japanese cars are cheap and easy to mantain. I have a 2012 Honda Fit as a daily that's a bit beat up from various fender benders my wife has been in, but mechanically is in fantastic condition. Every single part or fluid I've ever needed has been available very inexpensively from any parts shop, because 2012 Hondas are exceptionally common and have a high number of shared parts between models. There's very little excuse in my book for folks letting their cars literally rot into the ground as they drive the wheels off (sometimes literally, as the marks on the highway can attest).
Is the claim that /other/ costs have risen enough people are sacrificing vehicle maintenance? I think that /might/ be a fair argument, but I feel like ignorance is a much bigger issue. We have effectively no standards for issuing drivers licenses in this country, and most people are terrible drivers (just watch them, seriously) that put little attention or thought into their behavior on the roadway, and even less into the maintenance of their cars. Based on informal surveys, I find most people have never even read the owners manual that comes with their car, much less done basic maintenance themselves.
To be clear, I agree cars are expensive, and in many ways are the primary asset for most people because many Americans don't own their home, they rent. That car is what gets them to work, so it's essential for their economic survival. This means it's something worth investing in, ensuring it's maintained well, so it lasts a long time and performs well. But I feel like most people simply don't know anything at all about cars, and really have no interest in learning. It's very disappointing.