I think there is a generation of soundmen who believe the bass note is only struck at the same time as the bass drum. The bass is mixed as a low end rumble suitable only for 1/4 or 1/8 notes.
Unfortunately this is common. There are a lot of good sound techs and fortunately most of my experiences have been good. But, yeah, there some (a few too many IMO) who really don't really know how to mix a band. In my experience, bass guitar seems to be the first to get left out of the mix, but often times keyboards, rhythm guitar, and drums get poorly mixed to or completely left out. It seems that there is a "generation of soundmen" that will only give effort to mixing the lead guitar, kick drum (which is usually way too loud in the subs) and vocal. IMHO of course.