Illusory chocolate treats

I eat Kit-Kats quite a lot. Not in a "I only eat baked beans and Wotsits for dinner" way, just that if I fancy a chocolate biscuit, it'll most likely be a Kit-Kat.

Occasionally, you'll find that one finger, or even both, is missing its wafer and is basically all chocolate. And when that happens, I'm delighted. But why?

If I prefer "all chocolate" over "chocolate and wafer biscuit", why did I buy a Kit-Kat in the first place? Why didn't I buy a Dairy Milk or a Yorkie?

It's interesting, what we can convince ourselves is a bonus. Would they sell more if they said that 1 in every 1000 fingers had no wafer?