That is true. And these airlines never show up in the top half of the airline rankings. However, when flying these airlines you don't expect good service, and no one is going to proclaim that “flying is always a bad experience” because these airlines exist.

Personally, I have good experience with those airlines. As long as you are aware of the rules (print your boarding pass at home or use mobile boarding pass, limited carry-on luggage, usually doesn't go to the main airport) it's a good experience. Airplanes are relatively new, they are clean inside and the staff is friendly.