Perhaps a little less righteous indignation on your part, and a little more research, and you could answer your own questions....
Military Aid to the Civil Community - Wikipedia, the free encyclopedia
In this day and age when the beancounters rule everywhere, I believe that MOD has to be paid for any assistance by the other relevant government department (e.g. Agriculture if MOD helos are used to feed animals cut off in the snow). Quite often it is the OTHER government department that is unwilling to fund the costs - hence the MOD (for you read Army) doesn't get involved EVEN IF IT WOULD WISH TO!
Also, be aware, that Tesco employ far more people than are in the Army today. The Army is not the limitless pool of manpower people seem to think it is!