I'll always wonder if the climate may have been a factor. Baseball is a warm weather sport, and Boston -- in the Spring moreso than the Fall -- negates the concept, especially at night when most of the games are held. If the money is comparable, why wouldn't an athlete want to play in optimal conditions conducive to a long, productive career; Betts grew up in the South, after all.
As far as whether the franchise and/or city is undesirable, I did hear Mookie comment in an interview a year ago on the pressures of the full-court press and fan attention in Beantown as opposed to other places. LA is just so more relaxed in so many ways.
But all Red Sox fans should call BS on Betts' latest take on preferring the Dodgers because they're winners. Was he not on a team that finished first three straight years, including a World Series title and best record in club history?