It's too bad, because the best managers I've worked with were not good ICs, but they did multiply the effectiveness of the ICs they worked with, and so were absolutely invaluable to the company in a way that may not have shown up on paper. If those people exist in FB, as I'm sure they must, then they'd presumably get jettisoned as a result of this choice. That would be bad long term. I used to despise managers, until…
IMO the easiest way to solve this issue would be to normalize ICs making more than their managers. That way, only the people who really want to be managers are managing.
I have been a senior/principal engineer, as well as a director/senior director. The fact is that being a manager or director is just fundamentally a much harder job than being an IC. It's not that it's inherently more difficult, it's just that the day-to-day is much more of a grind than being an IC. For people wondering why engineering interviews can be so obscure/difficult, it's often because the cost of a bad hire can be catastrophic to a manager. I had a great team of about 30 people, except for 1 person who just couldn't get along with others. I spent about 80% of my energy on that person, and it sucked.
So for people wondering why managers get paid more, it's just that it's a shittier job that fewer people want to do than program.