I'll go with:
our major supermarket chains insist on placing two avocados on a plastic tray and wrapping them in cling-film, which does truly defy logic, as I am sure there is nothing they need to be protected from in your average supermarket.
.
Probably serves two purpose. First to keep assholes from squeezing them to see if they are ripe, second to make you buy two when you only really needed one.