Alcoholism is a mental illness and can have comorbidity with other mental issues. For many the answer to your "why am I holding this beer" is "I don't want to feel". But the alcoholic (not in any sort of recovery) never gets to the self reflection where they ask themselves why they have the beer.
Like many mental illnesses, the inability to have agency over certain thoughts or thought process is what make it an illness. Alcoholism and other addictions are not typically something people reason themselves into with compelling arguments and a cost-benefit analysis.
It's the same thing with intrusive thoughts - medication plus cognitive-behavioural therapy works best, that condition is something that you can reason yourself out of when you recognize the signs quickly enough.
This happens far less than you think. Alcoholics and other addicts will seek out or only socialize with enablers. They will also seek out codependent relationships. They'll do it subconsciously because they don't want pushback against their actions.
Realizing they have a problem isn't helpful for most alcoholics. Realizing they have a problem is just another thing driving them to drink. An alcoholic's family falling apart is often just the first in a series of shitty events on their descent to their rock bottom point.
One of the big differences between alcoholism and other mental illnesses is drinking is viewed as a "normal" behavior. Unless you're counting their drinks or actively tracking their visits to a bar most people aren't going to realize the alcoholic is drinking more and more often than they think.
I know several recovering alcoholics. When they were drinking simply knowing they had a problem was useless. That's like an asthmatic knowing they have asthma and someone just expecting them to breathe better. It just doesn't work that way.