Originally Posted by
BABenchley
Probably because they are cross-checking doors, assisting customers etc. They are allowed to do so.
And it would normally be in the 10 minutes before departure and 10 minutes after "20 minutes to landing" where both periods are quite time sensitive. It would typically only be 1 or 2 traverses. During the main part of the flight I can see it would be irritating, particularly for WC-hoppers, so a few strategically placed items would normally discourage it.
CW also gets this too, and not just 787s.