The challenge is timing. Power is a relatively low share of the cost of a modern data center, but the length of time it takes for approvals and construction for solar means it would substantially slow down the construction vs. using grid+natural gas turbines which are faster to build and get approval for.
I'm 100% on board with charging data centers more for their power usage. They can afford to pay the extra costs. They would much rather pay in dollars vs. in time.