If you're all using the same wires, you're subjected to those problems even if you don't contract with them. So multiple suppliers doesn't fix the issue. It just introduces more suppliers who can have those problems.

That would destroy the entire grid and a lot of equipment. It's why texas had rolling blackouts a few winters ago, it's a fine balance between supply and demand to maintain stable voltage and frequency. Failure to do so can result in a LOT of damage. If you don't have enough supply, you have to reduce demand.