This is what the Danish politicians did:
Selling a certain number of EVs per year in 2014 and 2015, the sales figures were increasing rapidly (with the introduction of the Model S especially).
Then they figured, ok, it's taking off now, so if we introduce a tax on it, we will get such an amount of tax revenue - amount of cars times the new tax. Despite warnings that people just might not want to buy as many EVs if they are heavily taxed, they put it into the budget as such.
Now, in the middle of 2016, they are like "Oh, what happened? People don't buy EVs any more, so we are not getting that revenue we thought". They are either very stupid and ignorant, or playing so on purpose.
Paid and sponsored by the Danish fossil fuel industry (possibly also some support from ICE car sales organisations?)