German Power Slips Below Zero as Negative-Price Phenomenon Grows

It would be rational to do that only if that could be done profitably. It usually can't be profitable due to large fixed costs that can't be paid for by the sale of the stored power.

Unfortunately the investment costs of storage are high, when you sell stored energy you still compete against other marginal energy producers, and the free power needs to be available often enough to be attractive.

The same argument occurs for Bitcoin mining: the fixed cost of the rigs can't be paid for by the value mined during the few hours of free-power operation.

Instead of assuming the market is irrational, you are better served by investigating your own thought processes.