It is a cynical BAA ploy, but then without people buying things in their shops, and the astronomical rents BAA can charge as a consequence. BAA would no doubt charge even more for landing fees and that would affect our ticket prices as passengers.
On the point of the journey to the lounges, it’s really only 30 seconds to the Galleries Lounge from North Security, and from South Security to the First and Galleries Lounges takes exactly 2m 37secs (if you go down the escalator in Harrods). I know because I have timed it!
Though it is a hassle with all the escalators, I would actually struggle to name an airport with a shorter time from clearing security to being in the lounge, so one must retain a sense of proportion about it all.
And let’s be honest, many people do like a little browse through the shops when they fly, especially on leisure trips.