What if I only want one?

Sign at City Pizza, Kelowna

I was riding my bicycle home through downtown Kelowna over the weekend and saw this sign. Now there is nothing unusual about selling pizza by the slice, in fact it is quite common these days.

My problem with this sign is that it seems to compel me to buy multiple slices. Do I really need to buy more than one slice? Or are there lots of different varieties of pizza that are sold by the slice. I'm confused, and confused customers don't do much shopping. Never good for a retailer.