So much of the industry is caught completely flat-footed, and projections and modeling are tweaked and changed until the projections for solar, wind, and storage, are often out of date and wrong by the time they are published.
Utilities are used to planning with five year time frames, but they will often use estimates from publications that are years old, and the publication may have been under review for a year, in addition to data collection time. So it's not unusual for utilities to do planning with numbers that are 10 years off of where they should be. It takes private citizens to cajole utilities and Public Utilities Commissions to practice basic good decision making.
There are two exceptions to the complete lack of innovation in the industry: Renewable Portfolio Standards that force utilities to change their production by force of law, and open markets in places like Texas where people can see how bad the decision making is from the old school and outcompete with their own generation sources. (and each of these states has had their own planning failures, both connected to improper governance at the PUC level, which is likely due to captured regulators.)