Economics. No one lives 150 years, so why pay for someone else’s roof when you’ll be making payments for so long.
Also even if you personally don't live that long, it does affect the value. For example a 99 year lease on a property is considerably less valuable than a 999 year lease, even though very few people live more than 99 years.
Given shingles last between 20-30 years someone's got to pay the cost of re-roofing on a regular basis throughout the house's lifetime
Then you've got the added maintenance, flammability and other downsides of a shingle roof to take into account too