For large web apps this is (and has always been) true. But the issue here is altogether different.
A large shared webhost has many thousands of web sites and only a few of them are active at any time. It is unreasonable to keep thousands of idle PHP processes around (and that is without room for concorrency which would be required in production).
That is what the web hotel business is all about, very cheap hosting, and this is what made PHP popular.