50 codes an hour seems like a slow capture service to have coming though normally when I use to do such work was like 50 every few min or so. So for 50 per hour that is crazy slow.
its because everytime you submit one captcha it need 1 minute for you able submit again
Maybe to have improved work software, no doubt using some form of software to submit work and capture codes though it. Generally though websites takes lot of time to load and lots sites now have software to work though to get better results. Still tho is nice amount to be paid for 100 and $4 worth BTC