Question: "Why do so many drivers think it is optional to use turn signals?"
Answer: No one cares because the cops do not enforce the laws
Statement: "It really annoys me."
Comment: "Grant me the serenity to accept the things I cannot change."
Bottom line, for Yahoo!Answers, Cars & Transportation, Safety --
"... waiting at a light, and the idiot doesn't use turn signal ... I have to basically stall a bit."
Counter-wise, the idiot forgot to turn off his turn signal ... you still have to stall a bit.
Turn signal lights are totally useless. You cannot trust them on, you cannot trust them off.
This is why smart people ignore the lights. This is why the cops do not use their own.