Why might packaged pineapple contain egg, soy, peanut, fish, milk, sulphites, tree nuts, sesame, crustaceans, shellfish, mustard seeds, wheat? Here is the proof:



I'm a bit scared to eat it. What do they do to it?!
Although it doesn't explicitly say so, that's allergy information. It's just been processed in a place that also (potentially) processes those things, so it potentially contains a trace amount, which could be bad if you have a really sensitive allergy. It won't contain enough of those things to matter for any other purpose.

Often labels like that are written along the lines of "processed in a facility which also processes..." to make it a little more clear. The lists aren't usually that long, either; most facilities don't process everything. But as pointed out in the comments, a grocery store is a lot more likely to just have a single kitchen that possibly handles all kinds of things.