Sin taxes are suffering from a shortage of sinners

Isnt the point of "sin taxes" to offset externalities? If the externalities decrease then so should the tax. If governments are looking for a steady source of income then "sin taxing" seems like the wrong approach.

I think a common argument is that it is to offset externalities but in reality I've never seen a sin tax that is based on the cost of the externality.

The tax on cigarettes is not pegged to the expenditures on COPD and other diseases and etc.

Afaik, all sin taxes go into the general coffers so they can't really be based on externalities. Plus the fuel tax doesn't even pay enough for road repair never mind any externalities (especially considering there's often no sales tax on fuel).

Nope, not the only point. Just adding some cost / friction to the "sin" is a goal.

It's a signal that existing funding mechanisms are no longer capable of supporting governments demands. So governments have gotten very creative at "off label deficit spending."

Are there any governments anymore that are not grasping at the most improbable straws for revenue? (Actually, no, just typing this, there are quite a few. Just not the ones around me certainly.)