I will stick in my two-cents worth.
Several years ago, any old mom-and-pop auto-parts store would have IN STOCK just about anything one needed for his Ford, Chevy, or Dodge.
These seemingly knowledgable people could remember part-numbers and walk straight to the shelf/bin and get exactly the part needed and 99% of the time it would be right.
That was back in the good old days when cars/trucks had only been in production for fifty years or so.
Today, a tobacco warehouse could not hold 1/10 of the parts necessary for even a small town parts-store.
Besides the 1968 Chevys and 1972 Fords, they also have to cater to Kias, Hundais, Toyotas, and the occasional Studebaker.
Then, there are "Sport", "GT", "touring", and etc. versions of each make, all with different engines, drivetrains, and brakes.
It is a miracle that one can get the right part at all, let alone have it the next day.
Sad to say, but those old knowledgable parts-counter guys get bewildered these days just about as much as the blank-eyed punks that stand behind most counters.
The old guy might know exactly what you are talking about, but the punk can work the computer.
Sadly, the same trend has overtaken the tire business.
We have the largest tire shop in several counties; and, twenty years ago, it was highly unusual for us to not have something on hand to take care of anything that came through the door, be it a hand-dolly or a Gleaner combine, and anything in between.
Now, it is more often than not that we have to special-order the tires a customer needs.
The vast amount of new sizes is overwhelming.
Just naming standard wheel sizes, there are 13", 14, 14.5, 15, 390mm, 16, 16.5, 17, 17.5, 18, 19, 19.5, 20, 21, 22, 22.5, 23, 24, and 24.5" and on and on, with a bejillion varying widths and heights for every wheel dimension.
It is very common for a particular tire size to be specific to only one make/model of vehicle; thus, considering high volume sales are unlikely, nobody anywhere will stock a set in their warehouse.
It is not at all uncommon to have a tourist travelling through to have to stay in a motel for a week or more, while some oddball tire is found and shipped in.
It is also not at all uncommon to get a set of four tires with each of the four tires coming from the four points of the compass.
Greed has created this mess that has backfired on the very tire manufacturers who came up with the scheme in the first place.