While it's true 29 of 30 major league teams failed to win the World Series this year, it's not true 29 teams had unsuccessful seasons. If that were true, almost everybody -- teams, players, fans -- would be unhappy almost all the time. This wouldn't be fun. We'd all stop doing this.
We prefer to define success broadly around here, and to recognize success will look different for every team. How many of the 30 teams can claim 2017 was successful? How many GMs in March would have accepted, on their own terms, with the rosters they started the season with, under the limitations they had to deal with, the seasons their teams actually had this year?