Um.... because Boffs are generally lacking in awesomness otherwise? Also you don't get basic versions. You get the normal ones. "Basic" traits are a weak version the same way "Superior" traits are improved.
Honestly, it doesn't make a lot of difference. SOME, but not a lot.
It would make more sense to me if we began with basic versions of our passive traits, then as we leveled up they advanced to standard quality- at, say, level 20- then finally an upgrade to Superior quality traits at level 40.
But that kind of reworking of the trait system just isn't likely to happen.