The power grid was about 4 minutes from collapse, not a half hour. They got through more than half the grace period to bring grid frequencies back into spec before every generator in the state would start tripping off the grid. They came really fucking close to it, if they had a few more plants trip off or if one of the utilities was delayed in load shedding ERCOT may have become the first interconnect to ever do a black start.
On top of that, they found out a bunch of the black start generators in the state were not actually functional because of the storm.