Boss GE-7(standard) ends at 6.4k while GEB-7(bass) ends at 10k. I understand that bass player want more control for lows but why there is more control for highs?
Electric guitars are actually quite muffled instruments: most pickups start cutting off at something like 4 kHz (with 12 dB/8ve), and amp cabinets also don't go much further, with a rather steeper cutoff.
This is often desired, be it if you want a smooth jazzy clean tone or want to reduce string squeak at high-gain settings. And distortion creates a great lot of new treble frequencies, which is why a muffled guitar signal doesn't necessarily mean the actual guitar sound will be muffled. So, if most signal components above 6 kHz come from the amp rather than the guitar, it doesn't really make much sense to control that range with a floor pedal EQ. It does actually make a lot of sense to put a treble tone control after a distortion pedal, but those generally have a tone pot anyway.
Quite different for bass: here you don't want to rely on distortion to create overtones – distortion tends to overcompress the pulsating dynamics, and smears percussive transients (most obvious in slap playing).
Both modern basses and -amps are designed to preserve those transients: active pickups have much higher frequency range than the mainstay passive ones of electric guitars, and many amps these days have a HF horn build in. (And indeed, what the audience hears is rather more often than not a DI signal, so the cabinet doesn't even get a chance to muffle the sound). With that, and agressive slap bass part indeed tends to have more treble content than a screaming guitar solo!
This means both 1. it makes sense to have 10 kHz controls on a bass EQ, while it doesn't on guitar and 2. you might in fact need them to keep those high frequencies in check, if you find the bass and amp a bit too bright (though this should actually be possible with the tone controls on the bass alone).
Surprisingly, a lot of a bass guitar's tone comes from the high frequencies. Without them you can end up with synthesiser-like tone - very blurry and undefined - so being able to tweak the higher pitched transients from the slap, pick or finger plucking can be very useful.
With a guitar, it may be less common to need to eq the higher frequencies, and certainly more common to rely on simple bass, mid and treble controls.
Well, it's due to the build up of enharmonic frequencies that can accumulate within the mix. Although a bass' highest frequency range is around 5khz, there may be unwanted high frequencies lurking within the mix, due to equipment itself. This is easier to eliminate with an Bass EQ unit with higher frequency spectral control. Take a look at Sustainpunch's article on the best EQ pedals for good insight on the most suitable bass EQ processor for you.