grading and reviewing

so in academic life, the one thing I think almost everyone would agree is the most negative experience is grading papers - (or marking exams) - teaching is fun (lecturing, supervising) and research is fun (coming up with ideas, building stuff, writing papers, giving presentations) - even some admin (interviewing, teaching/research admin) is ok

but grading is really de-grading.

so why is it the, that so many academics also volunteer for reviewing (i.e. being on Technical Programme Committees, and on Journal Boards of Editors)??

I suppose the main difference is that at least some of the things one reviews for conferences and journals are new and interesting, whereas most of the things one sees for exam answers are at best correct answers to something we already knew.

But to be honest, the payoff is pretty small, and in exam marking, at least sometimes you get the pleasure of seeing someone do a neat slightly novel answer (or the amusingly awful answers of course)...whereas there's very little amusing about awful paper submissions to conferences... ... ...