Because for the vast majority of low houred guys and gals it is the ONLY way to build hours, so that either the airlines or a multi piston charter operator will look at you.
The rates of pay are dismall by anyones standards. I had many days where it actually cost me to go to work, ie: you get to the club and either the weather turns to pants or the student couldn't be arsed to pitch up.
One club I was employed by, even had the cheek to tell me not to bother to come in again after the last flight of the day. No written or verbal warnings, just on your bike old boy, we both knew that on the £10 an hour I was earning there was no way I would be able to fight the case
At least in my last club, the minimum wage was paid after hours spent on duty were taken into account. I really do feel that somewhere in the region of £5 an hour is taking the urine somewhat for such a skilled job.
Rant over because nothing will change in the near future.