Why Do Airlines Still Use Tractor-feed Printers?
Probably note directly related to aviation, maybe more to airports than airlines:
Well, dot-matrix printers are expensive, but durable and print at very low cost and finally carbon copies (two, three or even four) of forms could be created. And replacing them will require a lot of software adaptions. 
I‘ve seen airports using text-user-interfaces (TUI via terminals), which are often working a lot of better (fast and efficient to use) then usual GUI applications. New stuff, is not automatically good.