It's not that they "cant figure it out", its that its a reverse auction where everyone gets paid the lowest price that is needed to provide the last bit of capacity. Why should a solar plant get paid 20% of what the gas plant gets paid just because they are more efficient?

That marginally cheap sources like solar or nuclear get paid a large profit for each kwh is a good thing, it encourages more of them to be build and over time push out the expensive marginal cost of gas (and coal where it's still used).