It is not because of the Billy Goat Curse or Bartman Curse or other Cubs curse you can think of...
It is because it is not in the best interest of MLB, baseball, the Cubs, the City of Chicago, and probably some of Cub fans for them to win it all.
Can you imagine if the Cubs were to win it all. While the excitement in the short term would be at all-time high, over time this will disipate and Cubs will become like any other team without the championship drought and lovable loser tag put on them.
For MLB, when the Cubs are in hunt which is the best case scenario for MLB, interest in baseball is much higher. This is because are paying attention to Cubs to see if they can get it done or not, and baseball fans all over the world are watching even if they are not Cub fans and especially if their team is not in contention. If the Cubs were ever to win a W.S., this impact would be lost in the following years which bad for MLB and bad for baseball.
For the Cub organization, winning it all is no good. This is because fans come and support them no matter how much they win or lose. There is really no incentive to win it all. Just being close to winning it all is the best for the organization for max profits for the Cubs. If they win it all and lose their lovable loser status, then once the Cubs become bad again then the turnout and support would become awful.
For the City of Chicago, if the Cubs were to win a World Series could you imagine the sports riot this would create. They would have a mass concentration of drunken, overexcited Cubs fans partying like their is no tomorrow if they were to win it all. In this situation, a major riot is almost certain to erupt which would horrible for the city and they would not want that.
For some Cub fans, part of being a Cubs fan is rooting to see something that I believe no living Cubs fan has ever seen and that is for them win a World Series. A Cubs championship is considered so rare and precious that euphoric feeling of them winning it all would surely be one of the ages. Also, as having the designation as a lovable lover, we as fans can always make excuses for their losing and it will always be accepted by the general public because that is just the Cubs for ya and there is always next year. Also, for many Cubs fans if they did win it all, they would quickly lose interest in the team if they were to return to their losing ways. Where as now, most Cubs fans give the Cubs their unconditional support, and they are really the only team in MLB that gets that.
Anyway, there is my Cubs rant for the year...on to next year