What BJ said pretty much.
Hakumen likes to approach from the air, and he has gigantic hitboxes. Tsubaki's 2c works well against that because it has a good hitbox of its own. 2c fits well into her game of charging at neutral or after neutral too, which again has nothing to do with how good 2c is itself, except that 2c is good at fending off long range, big old jump/iad forward stuff.
Makoto has a high hitting 5a in addition to her 6a. It just works better in my experience.
I don't actually find tsubaki's 2c to be crap. It is good, but it is more that it has a key role in her game that makes it particularly important for her. Plus a lot of her other shit is so terribly lackluster it makes it shine even more. Rachel's 6a is, in my opinion, better in every single regard.