I don''t think it is true that all alcoholics drink because of stress, though it could be a contributing factor for some, though don't ask what percentage. I know that stress was the overwhelming factor while I was drinking heavily. I started drinking heavily at the age of 60 because I couldn't sleep because of worrying about my life savings going down the drain on a money-losing business. There were other major stresses as well. I drank for about 75% of the time for a 5-year period, but eventually got out of the stressful situation, and the urge to drink ended. I now prefer to not drink, and have no intention of starting again. Before the age of 60, drinking was a minor part of my life.
When I was in detox/rehab (4 times) there were some counselors who agreed with me that stress was the cause of my drinking, There were others that claimed stress was an excuse, and that I drank because I was an alcoholic, and/or had an allergy to alcohol. was carrying unresolved resentments, suffered from an over-active ego and self-will run riot. I tried the recommended treatment recommended treatment of the later set of counselors (join AA, go to AA meetings, get a sponsor, work the steps and pray a lot), with no noticeable reduction in my drinking. In actual fact, my life improved, and then I magically stopped wanting to drink.
My main point is: beware of making generalizations along the lines of "all or most alcoholics drink because of X, and the cure is Y".