Because it is not cost effective. Simple as that.
The problem is that we don't have enough demand shaping to shift night time loads to day time, and we don't have enough storage to shift production to overnight. The result is that daytime generation is regularly going into negative rates (you have to pay to put power on the grid, which melts the returns on your investment into solar.
As far as problems go, it's a good one to have, as it will eventually result in lower prices for daytime generation.
We have incentivized night time consumption. Base load generation (nuclear, coal) can't ramp up and down fast enough to match the daily demand curve. They can't produce more than the minimum overnight demand, but they have keep producing that around the clock. To minimize the need for "peaker" plants during the day, they want the overnight demand to be as high as possible.
So they put steel mills, aluminum smelters, and other heavy industry on overnight shifts by offering them extraordinarily cheap power.
That incentivized overnight load needs to be shifted to daytime, so it can be met with solar and wind. Moving forward, we need to minimize overnight demand.