> I believe this trend is a result of management culture and performance metrics that attempt to measure "impact", and correlate pay and promotions along those measures.

Meta's performance reviews are also heavily weighted for measurable impact.

I think that the reason why it's beating Alphabet in so many fronts is team culture. Most new product teams are small and have a reasonably flat hierarchy. It's easy to make impact that's both effective and measurable, and the amount of engineering time working in "useless work" is minimised.