The difference being that Infuriate costs nothing to use. It's just a free 50 Gauge. The Blood you gain when TBN breaks is offset by the 2400 MP you spend to use it. If TBN didn't cost MP, then yeah, we'd have a problem of people trying to break it on auto-attacks for a DPS gain. But as it is, that's not a problem. There's no reason to use outside of busters and periods of high sustained damage.