It's actually pretty simple. It is virtually axiomatic that any gov't program, once implimented, exists into perpetuity, and its efficacy is never actually examined. It is also axoimatic that any gov't program serves as a basic for creating other, similar programs, regardless of whether or not the original program actually achieved its stated goals.
So, some gov't entity (local, state, federal) bans free toys with happy meals/imposes a tax on soda/bans trans-fats/bans salt in the preparation of food. There is virtually no chance that the ban will be examined in two, five, ten or even twenty years, to see if it actually generated the revenues stated/achieved the goal of reducing obesity/whatever.
Sometimes, a program will achieve one goal, but in so doing, create another. IIRC, the S-CHIP expansion, for example, was funded in part by a fairly significant tax increase on tobacco products. The fact that such taxes are regressive aside, the tax increase will have the (unexpected, but happy) benefit of reducing smoking. Of course, that means that the S-CHIP expansion is underfunded (fewer smokers, people smoking less both mean less tax revenue, therefore less funding), so the solution will be a tax on something (either more on tobacco, or possibly some other sin tax - soda, HFCS, whatever).
