All mine failed to grow.
Sorry to hear that. I had the same on my first attempt. Someone suggested that they might have been sprayed to prevent sprouting. I then washed the next batch very carefully several times and got them to sprout. Now they produce seed and multiply into 2 to 4 new onions.
The best size I get from seeds, but only one bulb per seed obviously. It would be nice to get them to split into more bulbs and larger bulbs, but I understand they are commercially grown from seed.