The phrase "discount carriers" refers to airlines or mobile phone companies that provide services at a lower cost compared to traditional carriers. Full definition
My guess is that the travel portal is suggesting flights on a larger carrier, which probably cost more in money and points than similar flights on discount carriers. (creditcards.com)
Though one thing I've found is that despite some horror stories, our strollers have always been treated kindly on airlines all over the world — discount carriers included. (havebabywilltravel.com)
Domestic airline flights are much more attainable in terms of mileage reward redemptions, both on the major carriers and on discount carriers. (creditcards.com)