I think 3 basic trends are at work:

1) We humans can look back at a long evolution in which trapping played a considerable role. It needs little capital input, a generally relative small amount of labour and profits greatly from intelligence and knowledge. Overall it could provide much vital return on the investment.

2) The technological progress and economic development have vastly increased the potency , availability and variability of the toolkit.

3) Small, protracted wars, especially with a vastly stronger side provide a set of circumstances which lets the weaker side gravitate towards the `trapping` approach.

There are of course lots of other variables like topography etc involved but the basic trends should pretty much look like that.