"even the rich FANG types"

I think you wanted to say "especially". You're exchanging clearly measurable amounts of money for something extremely nebulous like "developer productivity". As long as the person responsible for spend has a clear line of view on what devs report, buying hardware is (relatively) easy to justify.

Once the hardware comes out of a completely different cost center - a 1% savings for that cost center is promotion-worthy, and you'll never be able to measure a 1% productivity drop in devs. It'll look like free money.