Many people do... and they're not necessarily bad divers. eg Tomasz at Sidemount Silesia..
Yeah, I don't think it makes sense to wear a helmet in open water. I also don't think it makes much sense to dive AL tanks in cold water. I think people that dive this style copied their style from youtube videos but they don't understand why it makes sense in Mx but not in nothern Europe.
To be honest, most of the Sm Silesia video just show playing around in a pool, IMHO.
They are nice videos, but his style is not practical.
If he would make actual dives that required this much gas, he would be using 18L or 20L steel tanks instead of 6 or 8 AL tanks.
Think about it, 2 18l steel tanks hold almost as much gas as 4 ALs, and they are more streamline, need less room and you still have more space for stages.
Try to do a real dive with 8 AL tanks... than try to dive large steels with stages and you will see it much easier. The helmet is only there for show, IMHO.
And look at his backup lights, they point to the side... what for? It does look good on picture, that's my guess.