The question is asked every year, and the answer is marriage. Royal marriage.
The first Oktoberfest was held in October 1810 in Munich, Germany, in honor of the Bavarian Crown Prince Ludwig’s marriage to Princess Therese. The celebration lasted a full week. Over several years, the festival expanded to several weeks. Because Bavaria tends to get chilly in October, the festival was moved forward into September. To this day, Bavaria’s three week Oktoberfest begins in September and ends the first Sunday in October.