Why do people even become exam invigilators?

Like at my school there’s quite a few of them around during different exams and I’m just wondering why? I get marking exams but I don’t think anyone’s thought to themselves “when I grow up i wanna be an exam invigilator”.

Like do you get paid year round or only for the periods of time you moderate? As you’ll have about 3 seasons/4-5 months of work so do you get 7 or so months off? It’s just very confusing, like why do people wanna be one?