You're absolutely right that "it doesn't have to be that way". I don't know if its because everyone who wants a bike already has one (and thus re-selling isn't profitable) or if its because Denmark has fewer drug-addled fiends per capita, or if its because the cost of the grinding wheel to cut a u-lock exceeds the illicit resale value of a bike.

Whatever the case... a good ulock doesn't hurt even in Denmark.