I've been both an IC and a manager at FANG.

In some cases the work is terrible, an example is CloudFront at Amazon. It is a weirdly badly run organization which causes heavy operational stress on the teams that support the service and which is not sufficiently staffed to deal with the load. I don't know how it got into such a large hole.

More commonly, at least in big tech, is that the person has reached their Peter Principle in software (they may have other traits, like being a creator or whatever was in the article that allow them to succeed in other fields) and that is causing them tremendous stress, usually without them knowing the root cause.