That solution is more elegant, but it requires more political finesse. Measuring the external costs raises many difficult questions. What to do with that money

That solution is more elegant, but it requires more political finesse. Measuring the external costs raises many difficult questions. What to do with that money raises many more (hopefully not as difficult) questions. It is also a more general solution, which naturally threats more interests. All this makes it take longer to implement and makes a lot more people interested in prolonging it even further. Which raises costs and drives the best talent away, and makes it more likely the project gets killed. Throwing some pocket change to a few talented individuals and hope for the best is nasty hack, but sadly we lack skilled and properly motivated politicians to do much better.