How come no one can be a FWB?

I am a firm believer that if two people are good friends, but are alone but still have proper human urges, they should be able to hook up as long as rules and talking about it enough happen first. I'm not very lonely, I have a lot to keep my busy, but it'd be nice to feel someone else from time to time. Does anyone else feel the same way about being FWB with someone?