What can
Maybe a bass is just a lower range guitar, but most bassists (myself included) would dial in a very different EQ than most guitarists would, all other things being equal.
I have a few rig options that I sometimes play guitar OR bass through and find it interesting that I like about the same EQ curve on either instrument.
Not trying to be contradictory; one factor there is I play a P with flats, finger style, so having some "bright grit" at the amp helps with rock tone.