The loss of men with the fall of Singapore and the Philippines was a tragic waste. Both allied armies got themselves bottled-up with no place to go and no hope of relief. It has, of course, led to much finger-pointing ever since. The Japanese were ready, the Allies weren't. As RS has pointed out elsewhere, the British were busy fighting for survival in Europe. The Mediterranean was, arguably, the best/only way of taking the war back to the Axis forces given the limited resources available to the British after Dunkirk. There was also the battle for the Atlantic to consider, which was incredibly important. Arguably more so than the Mediterranean. Plus there was the strategic air campaign over Germany. Much was being done by a small nation punching above its, then, weight.

I like to think of the retreat to Dunkirk as a withdrawal. Never easy when the enemy is in hot pursuit. The BEF hadn't been broken when Gort ordered the retreat (the main thrust of the German assault was elsewhere), so I wouldn't be tempted to describe it as running away or a rout. Of course, the operation was hampered by the numbers of refugees on the roads, exacerbated by the Luftwaffe. So much so, that many units were forced to abandon their heavy equipment in order to make any progress.

The large scale operations in which Allied forces retreated in other theatres mainly came about by direct enemy action. Greece, Crete, Philippines, Malaya... Of course, another massive retreat which led to a reasonably safe haven, and a base from which to strike back, was that from Burma to India (when discussing the fight back through Burma, and other theatres, and the subject of manpower, it would be remiss to ignore the enormous contribution of the Indian Army).

Interesting concept, retreating and then striking back. Wellington did it for several years in the Peninsular Campaign, again, mainly on account of limited resources. With Manstein, in the East, it virtually became a doctrine and was continued by NATO during the last Cold War.