Why are Shaco players so bad, when I want them to be good?

I'm the kind of player that has lots of champs because I like the diversity. I play a mean support and capable jungle, but I like to try a plethora of different champions, in all the positions. But I don't pick a champ until I've practiced them a fair amount.

Shaco, is somewhat of an anomaly. He's mysterious, unconventional and his kit would make one think that he is potentially terrifying, but most of the time, when I see a Shaco on either team, he plays like someone who consistently took excessive blunt damage to the brain-pain as a wee child.

In my 3 years of playing League of Legends, I remember on 2 distinct occasions watching a Shaco player mercilessly bend the enemy team over an axe-grinder and have their way with them. These few rare occurrences have fooled me into thinking that when starting a game, someone chancing the wild-card, unpredictable Shaco pick has given us an edge!!! Alas, inevitably, after giving up 3 easy kills in the first 10 minutes, I have already put said, cretin-Shaco player on mute and am screaming in my own brain-pan, "Why are you doing the things that only a person who is a stupid person does?!?!" We then go on to lose the game as Shaco ignores objectives, refuses to ward, gets no kills or assists, and generally Shames the good and potentially devastating name of League Of Legend's only Jester/Harlequin champ.

Where have all the good Shaco players gone, and why are people with little to no skill consistently tempted to play a complex and potentially powerful champ only to fail miserably? You're not mysterious, you're not "The Crow". Play a reasonable champ until you have the brain-smarts to play an unpredictable anomaly like Shaco and unleash ferocious psychological terror on your foes the way only a demented harlequin can do.