It's just a matter of economics. Where the costs of bugs in production is low, which is probably the vast majority of the software out there, extensive test coverage simply doesn't make economic sense. Something breaks in some niche app, maybe someone is bothered enough to complain about it, it gets fixed at some point, and everybody moves on.

Where the costs are high, like say in safety critical software or large companies with highly paid engineers on-call where 9s of uptime matters, the amount of testing and development rigor naturally scale up.

This is why rigid stances like that from "Uncle Bob" are shortsighted: they have no awareness of the actual economics of things.