Another reason someone might not wear their wedding band is weight gain or loss. The band can be re-sized, but for someone constantly struggling with their weight it would not be a solution.
If I were married, I doubt I'd be able to wear a wedding band. Just could never feel comfortable with jewelry against my skin and didn't have anything to do with allergic dermatitis in my case. In HS, I didn't want to buy a class ring for that reason but my mother insisted. I haven't seen for decades and don't even think about it until something reminds me--like this discussion.
So, there are multiple reasons why a person wouldn't wear a wedding ring. Most are perfectly legit but there is that exception. :/