Having zero/negative prices incentivizes programs to incentivize consumers to use energy storage to get cheaper prices. Anyone who uses AC/heaters has at least their residence as a thermal battery and people can do things like shift when they do energy intensive activities as well.

Also, if you want enough power generation to power through the evening, then having excess generation during the peak generation hours/days is the expectation. When building new solar/wind is less than half the price of building any other form of energy production (even before considering the externalities of most of those other forms of energy production), its still cheaper to “overbuild” by a factor of two to reduce the need for other sources of power and provides the expectation of excess power needed to justify building storage.