[hguant]

The penalty for having an allergen present is steep, and the process of certifying that yes, you are in fact allergen free, is expensive and difficult, while the cost of adding an allergen into your process, for pretty much any foodstuff, is cheap, and the cost of slapping a "may contain peanuts" label on is cheaper.

I believe the original comment was complaining about the perverse incentive there.

[Ekaros]

And if may contain is not enough or allowed, may as well throw some amount of peanuts in and list it. And cover all the bases.