Quartz countertops are more expensive than natural granite. They're only cheaper than something like Marble.

Quartz is also strictly a better material: it's not as porous as granite, much much harder than marble (marble can be scratched so easily), and can be made into almost any color or pattern.

Super rich folks may prefer natural stone, but not because it's a better material... it may be preferred because it's a worse material in many cases. The cost and fragility is part of the allure by itself.

it's more stain resistant but it's an unnatural engineered material.

What does that have to do with anything? It's a better material. Many materials are engineered to make them better. Steel isn't 'natural' either in that regard.

Natural stone contains silica too, so it's not clear that these workers would be silicosis-free if they'd been cutting e.g. granite instead.

Average granite is 72% quartz:

https://en.wikipedia.org/wiki/Granite#Chemical_composition