What happened was probably the classic case of unfinished business.
What happened came about as a result of the situation Germany had been left in at the end of WW1. Arguably, from a British point of view, that came about as a result of the treaties we had made with France in an effort to maintain the balance of power in Europe and the arms race which accompanied such treaties. Obviously, the factors leading to WW1 were varied and complex. After the slaughter of that war, many in Britain wanted to make peace permanent. As a result, Britain was ill prepared to become entangled in another European war and even less prepared for it to go global.
As the war progressed, the majority of British Imperial troops and units, mainly consisted of citizen soldiers who, unlike those troops of their enemies war machines, had not been preparing for war, but had had it thrust upon them. Whether or not one considers it a shame I don’t know, but it is history and it is the history which has shaped the world in which we now live.