Faculty serve on the Senate for many reasons. For some, it is out of a sense of civic responsibility. For some it is an opportunity to participate in shared governance of the university. Others serve because they have an axe to grind. The only reward we receive for this activity is our ration of cookies.
Faculty teach classes because that is the primary job at an educational institution.
We all know that teaching is its own reward. Faculty do scholarly activity because that is the primary job at an educational institution that has a research mission. Faculty undertake scholarly activity because that is the reason most faculty obtained advanced degrees and their potential for continued scholarly activity was the main reason most were hired at a research university. Faculty are promoted and receive merit raises on the basis of their scholarly activity. Faculty seek extramural funding because that is the best way to fund their scholarly activity.