Boz
The sky won't fall in just because a few events are cancelled for 10 days.
The Last Night of the Proma is a jolly loud event which is not recognised as appropriate during a period of National Mourning.
It is a case of Respect with a capital R.
There is no way that the majority of events can be re-arranged this year, let alone in ten days time.
Bookings of venues, caterers, etc. have to be made way in advance.
Performers / participants, competitors, vendors etc can't all suddenly be available again at the drop of a hat, so all the effort and expense already incurred by many thousands of people is now totally wasted or lost.
How about a bit of Respect and sympathy for them?
After all, anyone who wants to mourn can still do that.
Think of the effect on our beleaguered economy too of all these cancelled events!