There were multiple conditions that seem to have caused the outages. (I say "seem" because not all the data is in yet. A definitive explanation might be weeks away.)
But here is the gist of it: When wind and solar power failed, it took parts of the grid below its "baseload" level, and that started bringing down parts of the grid. Period.
Wind and solar only work about 20-30% of the time. When they aren't working, there needs to be back up. Energy on the grid MUST meet the demand, or the grid goes down. In this case, the backup systems couldn't be brought online adequately due to poor maintenance, poor planning, and poor policy. Bingo! The grid started failing.
The backup necessary to keep the grid up for say, 30 days, if wind and solar went down, would cost about 1/3 of what it would cost for the wind and solar installations they were designed to back up. Consumers have been reaping the benefits of wind and solar only because these have been massively subsidized. The actual cost of wind and solar is expected to level out to much higher rates than from other sources if subsidies ever end.
I believe that wind and solar have a place, especially for niche markets like home and ranch energy independence, but the massive investment in Texas was a mistake. Politicians bought the solution without examining the Science.