For one, this would be a huge dps increase to the class, completely unbalancing it relative to warrior.

Secondly.. it would defeat the purpose of the skill.

Shield Swipe is a tp regeneration tool. Any gcd during which you use shield swipe you regenerate more TP than you spent on the skill. This is like, invigorate over time. Use of this skill is how you maintain your tp in long fights. It is also a dps increase, not that our dps matters much. Using swipe when its available will help keep your tp up enough to maintain fracture if you are so inclined. Obviously only do these things if you have enough hate, but you should, since warrior's take every other cycle off in terms of generating hate so they can debuff damage done.