Yes, I don't understand why this is not the solution.. They don't even have to raise it for everyone (ie. if they don't want everyone else to subsidise the cost to larger consumers).

If your workload is such that it causes grid instability, you should pay at least $X more for the service, where $X is the cost of grid instability.

This way if it's too expensive for big customers to run a workload which exceeds the capability of the grid, they'll go elsewhere. This would incentivise the grid operator to improve stability such that they could better support the big customer's workload.