BPO means 'Business Process Outsourcing'. BPO jobs are popular because, it is advantageous to three sets of people. Who are they? Those who want to get the work done for a 'stated fixed price', without any escalation in costs, those who are ready to carry out the same for a stated fixed price and those fresh graduates and job seekers.
It enables companies to get certain works done easily without recruiting any people. People (companies) with 'administrative' acumen, recruit people for the same on a monthly salary which will always be very much lower than what the BPO organizations get for the contract. And for those poor job seekers who are in need of some job, whatever salary they get is a bonanza!