AFAIK, most amps have active EQs, not all have a passive low pass filter control.
It's a simple control that lets you mellow out the highs when you want to. Just because an amp has the same controls doesn't mean you can't have them available on the bass itself. The same could be argued about having onboard EQ. It gives you versatility from the bass itself.
It wouldn't be a good idea to have more than one tone control on a bass, because tone controls run parallel to the signal path, so when you have two, they will both act as master tones whenever the pickup volumes are equal.
Having separate 2 or 3 band EQs per pickup would also be absurd. How often are you really going to be EQing the pickups differently? (Unless you have dual outputs.)
