The Gentleman Grafter

Also, eye contact is subliminally threatening. That's probably not good for sales, particularly in a big city like New York, where a stranger who approaches you and makes eye contact activates the Shields Up response. (The odds that he is about to ask you for money are really, really high. Especially if he starts some big, rambling story instead of just immediately asking you for directions.) Moreover, scaring people is not something you want to do if you want to have a decades-long career, in one neighborhood, doing something that is technically illegal. One's first on-street encounter with a squatting, potato-obsessed geek with a knife in his hand is probably scary enough without having to know that he's looking at you.

Finally, I'd guess that eye contact is risky because it turns the show from a monologue into a dialogue. What if the mark starts an argument? Or runs away in terror? How would that play to the rest of the audience? Even a friendly chat could be bad for business if it takes up too much time that could be better spent running the spiel for a fresh set of passersby.