On-prem is almost always much more expensive "in monetary terms" when you take into account the cost of staffing the operation needed to maintain those on-prem systems, especially if a company has e.g. compliance requirements etc.
The idea that cloud is obviously more expensive is not actually supported by the economics. If it was, we'd see people leaving the cloud in droves, for competitive reasons.
There are of course cases where it can make sense for a company to do on-prem. But they're about as common as the cases where it makes sense for a company to generate its own electricity instead of using the local grid.