OTAs have associations with airlines. When Online Travel Agencies buy tickets from the airline, they do that in bulk, thus saving themselves a lot of money. After that, they get to decide what airfares to keep (more or less). In this case, they can really lower the airfares to prove a point or build a reputation. On the other hand, airlines never lower the airfares beyond a point. That’s the reason why people prefer getting tickets booked from an online portal. It’s, however, a matter of chance and one must do the research.