Allegiant, Spirit Airlines and Frontier Airlines are all carriers that people love to complain about for their notorious unbundling pricing practices that make passengers pay for every little extra thing beyond a seat on the plane. But as respected trade pub Airline Weekly’s 2018 annual Global Earnings Scorecard makes abundantly clear, the complainers look to be giving these three ultra-low-fare carriers plenty of business nonetheless. All three of the aforementioned airlines wound up among the…