[lolinder]

A quick search suggests that it's because historically clay tile roofs didn't do well in environments that regularly drop below freezing (like Colorado). It sounds like newer materials can handle freezing weather fine, so our usage of asphalt probably is just a cultural habit at this point.

[altano]

Slate handles cold weather and lasts for hundreds of years. It also looks fucking awesome.

We don't use it anymore because it's expensive.

Also because no one knows how to handle it anymore and ignorant roofers will break your really expensive slate roof.