What's the best selling flavor of ice cream?
Because it's the best flavor?
Because vanilla is non-offensive.
Because vanilla mixes with everything while retaining the flavor of any other ice cream.
Because vanilla is the default choice when people don't feel thinking.
Because vanilla can be tolerated by most people in most situations.
Because vanilla is somewhat bland.
What's your favorite flavor of ice cream?
You probably can't find more than two people out of ten who would list vanilla as theirs.
While it would be hard to find any group that would overwhelmingly pick another flavor as their favorite - most would settle for vanilla.