Not all gas plants are made equally. There's a huge difference operation-wise between "able to scale at any moment from 0% to 100% within 15 minutes" and "can start going online within 30 days".

Most current plants are either designed to run basically all the time, or only run a couple of hours multiple times a day.

A renewable grid needs generation which is fully shut down for months, but can scale up to 100% within days when weather forecasts predict it'll be needed. The current plants might work as a stop-gap measure, but long-term we'll need to build something designed specifically for this application.