I work at a 1400 capacity venue.
For bass guitar if we're only using one channel, then we'll take a DI direct from the guitar. If we're using two we'll use a DI along with a microphone to the cab.
If a bassist specifically asked me to take DI from their rig then I'd have no problem doing it, it's just I much prefer to do it this way. Why?
-Protecting against failure of the amp
-Musicians will often be changing settings during the show on an amp, this will of course affect the DI coming to the FoH and mean constant adjustment down this end as well
-A DI from the amp will be EQed for THAT amp and cab, not for a FoH system
That's why.