Unconscionability.
I think this is the actual issue. Personally, I always go with a fixed rate because I want to attempt to budget the expected cost as much as I can. Also, I'd be pretty surprised if it was actually a good deal in the long run, because there are periodic squeezes that happen when individual stations are taken down for maintenance.
I seriously doubt that people are ever informed that there is essentially no limit to how much they can be charged per Kwh as we saw over the past week. It's essentially like the futures market. You can save a cent or two per Kwh, but the potential is there for essentially limitless charges on the other side. IIRC, similar things have happened before when things went badly sideways on the production side, but probably not in such a widespread way, a least in Texas.
Some will say that it's the consumer's own fault if they are uneducated about the risks. I can sympathize with that viewpoint a bit. I think these contracts need some kind of price banding where the range of pricing could be as low as half, to as much as double or something like that, but since they are written by the power company in an attempt to limit its own risk, that's not going to happen.