Afaik, the way abnormal situations like these are handled in northern Europe is that the grid suppliers have agreements with the very large industrial consumers (think aluminium smelters) who agree to shut down immediately when the grid frequency goes below a certain trigger level.

The way I understand it, this is useful both in time-critical emergencies (like keeping the grid at 50 Hz when a nuclear plant suddenly goes offline for some random safety reason) and when things are moving a lot slower, like during periods of extreme colds and extreme electicity demand from heating houses.

So, this approach is useful in removing the need for rolling blackouts, at least until demand reaches some very extreme level, but it does require ahead of time investments in shutdown agreements.

Perhaps Texas hasn't been in this extreme situation before, and they simply don't have enough industrial shutdown agreements in place?