Because coal plant retirements (and the coal deliveries those plants require) are planned quite a bit in advance. Average electric bill will go up $15/month (~4%) in the interim (not trivial, but also not catastrophic). It’s a political issue to subsidize that unexpected short term cost, not a technical issue to keep an aging plant running.
Energy transitions aren’t easy. There will be missteps.
(I would agree the local and or state government should provide support for low income electric users impacted by this until rates come back down from more renewables online pushing out oil generation; cut the utility a check and define the means testing)