They are. It's just most urban people don't bother with them anymore because the electronic ignitions and fuel injectors make ICE engines very reliable starters even in quite cold weather. My, now eight year old vehicles, still start reliably at -40F even parked outside because I know I will be faced with those temperatures every year and I keep them well repaired to handle that.

Mostly you will see block heaters on diesels and older unreliable cars. And yes, they do work very well and are a cheap insurance policy for getting your car started.