Because that is considered more and more unpleasant by customers, though, I find interesting that here it Italy it is more and more common to see waiters walk to your table with a wireles card-reader and perform the payment operation there in front of you (I am referring specifically to CC payments, that is not requiring PIN)

Sure, one may argue that some waiters may have excellent visual memory, or that the wireless connection from the mobile device and its base is not secure (enough), and what not.

But security is not a yes-no concept. There are defferent degrees and I too would avoid decreasing it as much as possibe. I guess I would not entrust my CC details to similar systems either.