Passengers were given chewing gum to alleviate pressure on their ear drums on takeoff and landing. Airlines had to stop the practice when clean up became too expensive.
In the early days of passenger flights airlines took great care of their customers, providing them with customer amenities packages that could include the gum, toothbrush and paste, shaving essentials, pillows and blankets.
As operating costs rose, these packages got smaller and less comprehensive, and are now rare. Security concerns in the last decade have also reduced all items available during a flight.
The gum was included in the package so that passengers could resolve the problem of changing pressure on body parts containing air (mainly ear drums) that resulted when the plane lifted higher or dropped lower on takeoff and landing.
Unfortunately, all this chewing gum did not reach a suitable waste bin after use, and was found adhering to almost every surface in the cabin.
One airline is now banning gum in the passenger cabin completely: