My first legal street motorcycle was a Yamaha Maxim 650. It was my only bike and I rode it everyday, as hard as I possibly could. I bought a rear tire every other year. Fast forward thirty years I have multiple cages multiple bikes (although for some reason I try to take the RIII everyday
) I am now purchasing three rear tires for the RIII yearly. I know the factors that contribute to tire wear, I know it was a lighter less powerful machine. But so what? Tires are made to last 40-100 thousand miles on a vehicle with double the torque, three to four times the weight of any motorcycle. There have been many developments in the car tire industry over just the last 20 years. There are substances put into the rubber compound that make the tire grip better and last longer without having to make the tire softer or harder etc. etc. Car manufacturers do not put all of this technology and development into motorcycle tires because it is not cost efficient as compared to the enormous sales of car tires. Plus why should they when they have so many happy idiots willing to pay $300 two, three or four times a year for a motorcycle tire with 20-plus year old technology.
P.S. you're correct about the dealers every time I have needed a tire no one has had that tire in stock. And they never will.