your right, they dont have a choice but they ride safely. Why shouldnt cyclists also ride safely? Because we have ears can we close our eyes?
A lifesaver is a glance down to your side before any change in speed or direction. Not so much a look behind but a glance to your left if turning left and right if turning right. Anyone can ry to nip past you last minute, a lifesaver means your aware at all times. It also tells people behind you that your about to do something, makes em think. It does not replace looking fully behind, in fact my lifesavers tend to do both, with practice they become quick and part of your style so you dont notice them
try it