»In praise of the chainguard

I wonder why chainguards disappeared from most bicycles. A nice, sturdy chainguard on my commuter bicycle would make a huge difference to keeping my cuffs clean, and also maintain a sand- and muck-free chainline. Many older and "leisure"-style bicycles have chainguards; why doesn't my Bianchi?
And to balance a rare, positive thought, I read all over the internet today that Karim Cycles got busted for running a fencing ring. Bicycle theft on the Berkeley campus should go down appropriately.