Base load power cannot provide predictable rates because it provides a fixed amount of power that the market then bids on. If there's too much demand rates go up arbitrarily high. If there's too little rates go to zero.

Dispatchable power is the only sort of power that provides 24x7 power with predictable rates. If there's more demand, you produce more power (at the same cost). If there's less, you produce less so you can sell what you do produce at the same cost.