It is purely because it is an easy option and the airlines will foot the bill. Many many many more people are killed in automobile accidents every year so if the health and safety people say it will save lives then suggest every car/truck and bus has one installed. Trouble is this may impact on the profitibility of auto industry so would never get sactioned.
If there was a cost trade off then perhaps be a good idea. Line checks, simple, send in the tape. One line checker could do about 10 a day