Awful reason, but fuck these laws. Declaring a person forever disqualified from what other people will still be allowed to do is obviously not the same thing as 'you must be 18.' It is infuriating how many people pretend there's no difference.
Ban smoking for everyone or don't ban smoking. Trying to be "clever" about equality under the law is just fresh discrimination.
You want money? Tax the companies, not the customers. Take as much as you like. The alternative is, they don't get to exist.