They've talked about this at length in both blog posts and podcasts. The gist is that all the Amazon cloud stuff still took effort, their ops team is essentially the same size and they're actually saving all this money.
Also the AWS cloud engineers are so much more expensive because the AWS learning treadmill runs at a 10x speed compared to the on-prem one.
Our cloud engineers spend so much of their time simply keeping up with all the things they need to keep up with, even for workflows that have been running just fine, for years.
The on-prem engineers also need to be up to date, but the changes are more measured and easier to manage.
