Big top down push to move to public cloud, basically no thought to operating expenses.. and now theres a ton of low hanging fruit. Most of these same firms have very little ability to measure their costs in a timely, granular manner, and so put in only very blunt processes to try to limit costs.
Last org I was at could probably re-allocate 10% of engineering staff using the cloud to a SWAT team finding cloud cost saves for 2 years before they ran out of stuff that costs 5x their salary to get fix/optimize/kill in the cloud.
A lot of the same orgs CTOs sold themselves on the idea that they'd need less infra people in the cloud. This really has not been the case, and more often the cloud infra people are more expensive too. Meanwhile many need to permanently maintain an on-prem footprint for latency/legal/legacy/etc reasons.. so you end up with net more staff.
I know a handful of Wall St firms that are moving a lot of "big data" type use cases back out of the cloud because its hideously expensive for their use cases.