Oh man, where to start?
For some people it's just totally addicting. Honestly, when you got a band behind you and everybody's firing on all cylinders, interacting like one big rock and roll organism, the rush is better than booze or dope or even sex.
Not that I'm experienced with dope.
At any rate, over the years I deveolped into a stage performer. I was never partiuclarly interested in being a great technical player to begin with (genres specializing in that as a requirement tend to bore me to tears) and after some years of being in bands I got to the point where I'm pretty comfortable on stage and can really rock out with no inhibitions. With a job and family if I played out every weekend it'd wear me down, but playing out about once a month is great, and when I go for for more than that I start itching to get back onstage.