Your reply seems to assume that companies are efficient. Which is not the case, and the larger the company, the lower internal s/n ratio and, arguably, the larger percent of wastage.

Also, "immediately" switching across cloud vendors is not even a pipe dream, it's an impossibility and the very act of switching is incredibly expensive both short and long term (unless your cloud usage is one VM or so). So there's no simplicity in that example, it's a counter-example.