Five reasons ...
- If cars were as wide as bikes then every road would be an 8 lane highway
It makes cagers very jealous (enrages some with jealousy)

It's lessens traffic congestion, pollution blahblah
It lets you sleep in min 15 minutes longer (or 15 mins more work, exercise, study whatever)
Because we CAN
In (fargnlarjnumba) of years commutting in Syd/Mel I have not ever, one, single, time been hassled about it by the law. Everybody expects it and would do it if they could (& weren't too scared to do nowt but drive a 5 seat lounge room around).
Enjoy what makes a bike great in the city.