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

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.

If this was processed at the store then there's a pretty good chance they process everything in close quarters where there is a reasonable chance it was packaged alongside some of the other store-packaged products that could contain some of these other things. I definitely would not expect fresh pineapple to include shellfish.

Haha, that's hilarious.

I suspect it's a catch-all legal disclaimer. Put "may spawn bank-robbing zombies" on all your food labels and no one can ever sue you when your zombies rob their bank accounts.

It's really frustrating for people with food allergies: They have to avoid all foods with half-assed legal disclaimers instead of just foods that to actually contain the allergen.