Functional Reasons: On the few occasions enemies line up and CAN be hit with a combo attack, you're doing so little damage by the third hit, it's barely worth the selection. W and ALL weapons get better results for cheaper and don't require any kind of skill or pricey investment. Very few combo attacks are actually worth the cost and the people who get it are disappointed to have such a useless skill (Zengar doesn't like spending that much for such bad results and Roa gives a hard metal facepalm for not getting Revenge).
Other Reasons: Continuous Attack, Continuous Action, Attack Again. Can we PLEASE get some more unique names so I don't have to check Akurasu every time we talk about these?