Not on the same scale but in my previous company we observed the same thing (though the other way around since we moved from self-hosted to cloud).

He had a team of 4 managing the infra for an app (82 million users, 30 million DAU) and spent around 500.000€ per year on the data centers + this team's salaries + some other expenses like travels to the datacenters, some new stuff etc..., let's say around 1.000.000€ per year.

At some point upper management decided to move to the cloud and we eneded up in a worse situation: the promise of easier resource management was unfulfilled since the same 4 people was managing now the cloud so no cost reduction on that side and most important, cloud costs were 4-5 times higher than self-hosting

I still wonder why management decided to go that way