Caddyman really hit on the problem, has any new car buyer ever asked the salesman how long will the CV boots last? No one does this. When people are shopping for a car, they are only interested in what they see, for the most part.
Sometimes a vehicle comes under fire for reliability in general, as American cars did for so many years. Manufacturers had to respond by making more reliable vehicles, in general. People began to notice that timing belts were an issue when the general population of new car buyers started keeping their cars for more than three years. Now timing chains are more popular, even though a timing belt could be made to last just as long and would be cheaper.
It does seem that CV joint boots are lasting longer than they used to. I remember having to change them about every 4 to 5 years, now it seems like 10 years is the new normal for them. It is just a matter of the type of rubber used. Urethane rubber would last much longer than the buna or latex rubbers often used. Silicone rubber would probably last the life of the vehicle and then some. BTW, I don’t think I have ever seen a boot split from road debris, the lower control arm and steering knuckle pretty much protects them from flying debris. They split from the rubber aging.
When consumers start asking the question, the manufacturers will respond. But keep in mind, if a long lasting boot costs say a dollar more, at 4 per vehicle, that $4 per vehicle. Now multiply that by 5 million vehicles that use these boots in their drivetrain, thats $20 million. If no one is asking the question, then that is not considered added value, only added cost.
If people are asking the question and the manufacturer figures out that advertising long life boots will add more than the $4 per vehicle in added value, then you will see longer lasting boots.