This is a genuine question as I really don't know the answer!
I am not technically minded, I'm not a sound engineer, I have never been in a band, so I really would like to know why so many bands make the most common of errors and that is 'I can't hear the singer, I can't make out the lyrics, I don't know what atmosphere you're trying to create, if your telling me a story then you're wasting my time'
I've been to some of the loudest gigs ever staged on the planet, Led Zeppelin, The Who, Ozzy, Pink Floyd, so it's not power as trust me you hear every word that Robert Plant is saying, so I know the sound engineering is possible.
Of course it might be the quality of their equipment and Lord knows the aforementioned acts can afford the very best, though some excellent local bands seem to get over this.
I'm cautious about saying that cover bands seem to do a better job of this but of course my familiarity with the material may be playing tricks with my mind and my head may be filling in the blanks that are reaching my ears.
Is it the personality of the musicians in the group making sure their instruments are wound up to volume 11 leaving no bandwidth for the vocals.
I know it must be harder to play an instrument than sing but I fear that these musicians must consider the audience needs when listening to a complete song and not just a part or two of it's construction.
Maybe it's the singers fault, maybe on the sound check they sing with confidence and then when the action begins then the nerves make them quieter or hold the microphone in a different way or position.
It would not be fair to name the acts I have seen that have this issue, all I can say is that it is the majority of them and I believe this problem will really hold back some terrific acts.
Trust me, those bands that get this right come across as more professional and serious than those that don't.
It's not even a question of value for money as a lot of the bands I see give their time and considerable efforts for free, it is that I want to see a band show me the very best of what they can do and in turn, like all audience members, I want to tell anyone I know who's interested in music what a great show you've put on and they must go and see them!