There are numerous pseudo-hub airports in the world where baggage security is sub-optimal. At these airports many of the locally-originating locals (even when not terribly wealthy and flying domestically) get their luggage wrapped or put into a plastic bag by default.
While incidence of theft at UK airports is low, if one is changing flights at one of these 'less secure' airports with a long layover, it would seem brave not to have had one's bag wrapped at your originating airport (e.g. LHR)