My perspective is that promotion especially for PMs (and SWEs to some extent) involves pushing novelty / "demonstrating impact".

IMHO this in large part responsible for Google's ADHD around project cancellations/replacements.

Not restricted to PMs but it is especially pernicious when product direction gets pushed this way.

Cost cutting and underhiring were never a problem while I Was there. More the opposite. They overhired and then there was no good throughput on projects because every chef was in the kitchen at once.

If I recall, the turndown on e.g. Google Reader was more about finding it difficult to get SWEs who wanted to work on it. I think it would have been increasingly difficult to survive the performance review cycle if you were stuck on a "backwater" project like that.