The BRM team seem to be pretty good at communicating with us, their customers, so no doubt they will be well aware of this thread but whether or not they decide to comment on what is clearly a commercial decision is entirely up to them and I happily respect their decision not to say anything if that is what they decide to do.
Overall it strikes me as a logical decision for several reasons. Firstly I think everybody must recognise that the 'Railway Modeller' has no equal in the printed model railway media when it comes to the diary items and setting out to compete with that would cost (staff) time, and money in terms of pages lost for either copy or advertisements. So in that respect it is probably a relatively simple commercial decision.
Secondly BRM, probably to a greater extent than the other magazines, is very 'web aware' and no doubt realises that the vast majority of shows are publicised by that route - in far greater detail than they could ever hope to emulate in a printed mag. True they lose the opportunity to 'catch' folk who would otherwise be unaware of a show but I bet that number is not very significant and in any case some of them will be picked up via another arm of the publsher, in the shape of RM web.
Finally all the 'mainstream' magazine publishers engage in reader research not only asking us what we like about their mag but what we want to see more, or less, of - which helps them judge how editorial space can be used to best advantage. But often such research also asks what other mags etc we read and we all know that still the Modeller tends to dominate the market so quite likely many who read BRM also read the Modeller - which neatly takes us back to the first point about the Modeller's basically unassailable position in respect of putting such information in print. I truly wonder how many folk buy BRM for the diary information?
Oh and as a possibly relevant postscript I really can't recall the last time I looked at the exhibition diary in an y of the printed magazines - I get all my information on shows from the web.