Alcohol and Anti-Depressants

It has been two and a half years since I had a drink of alcohol. First it was because I was pregnant, then breastfeeding, and then when I was diagnosed with postnatal depression and started on anti-depressants. Since I was never really into alcohol much, I don't miss it.

From medical advice and plain common sense, I have decided that I will not have a drink until I'm off anti-depressants. Which raises an issue I just don't get....

Why do people on anti-depressants continue to drink alcohol (and often by the bucketload)?

If you're depressed and taking something to help you not be depressed, then why undo all that good work by drinking a depressant?

I know some people might feel good by drinking, like they can drink all of their problems away.  But there are numerous warnings that while drinking might make you feel good in the short term, long term it can make the symptoms of depression and anxiety worse.

I don't ever want to return to that dark, dark place I was in last year. If not drinking ever again is what I need to do, then I am more than happy to do it.

Why take anti-depressants then nullify their effectiveness with booze?

I don't get it. Please explain...