Texas resident here. There's a guy who's been riding a Segway around my neighborhood looking for weather damage from recent storms, and his pitch to homeowners is that they don't need to replace the entire roof, just the section where things are--or will soon be--leaking.

It's probably more efficient to replace the entire roof at once, and insurers would almost certainly prefer the entire roof to be the same age, but asphalt does have some advantages for situations in which nearly every storm tears up just a few shingles.

I think the right question is why are roofs not already made out of high-impact glass? Did nobody ever think about this before Elon? Maybe.

More likely a glass roof is a net negative that has to be offset by the solar cells, making them less cost effective than otherwise.