I don't think those particular companies that instituted the hot tap ban had any direct thoughts about "it is not zero risk so we'll ban it", rather it was more like, during their infancy, they thought they had enough local expertise to attempt one or two and one or two went badly wrong. Hot taps are common and a bit dangerous, but can be really dangerous when you don't know what you're doing. TDW, on the other hand, can do them blindfolded in a coal bin.