[grosswait]

Economics. No one lives 150 years, so why pay for someone else’s roof when you’ll be making payments for so long.

[IshKebab]

Someone else suggested that you have to replace your roofs every 25 years though. People definitely live for 25 years!!

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.

[AngryData]

25 years is common but most places allow 2 or 3 shingle overs that don't require a tearoff. They just slap a naked layer of new shingles over the old which is even cheaper than the first roof/layer.

[youngtaff]

You're not paying for someone else's roof… it forms part of the house value when you sell

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