Because then every commit from now on has a ton of formatting changes that make it harder to see what was actually changed.
And Google uses P4(ish) because monorepo, so they build further abstractions over P4 to enable git and hg in user space which erases most of the potential benefits of either which is also all really, really good software, but it’s all effort necessitated by monorepo. CitC is a work of art, but it is also something necessitated by a stack of other choices that forced their hand into inventing something miraculous to keep hacking around a previous limitation that nobody else has.
That seems like way more complexity than just doing it once and for all. Now the commit log is littered by a bunch of automatic commits that format one file at a time.