'Cause it's not like there'd be music to listen to.
With the utmost respect, man, I just can't wrap my mind around how people feel the band has to be jumping around the stage and the audience has to be dancing or moshing or what-have-you. I'm certain most of us here spend plenty of time sitting or standing and staring while listening to music. What is it about having other people near you which suddenly makes this unacceptable?
Personally, hearing the band live, seeing the band perform the music before you (even if it's some noise artist who just presses a button every ten minutes), that's
all of the fun. Anything else is highly unnecessary and often detrimental. If I'm seeing a band that I'm only half into then I'll be moshing and headbanging or swaying, whatever depending on the genre. But if it's a band I really like, everything is focused totally on the music. No distractions.