Well technically the year 2000 was the last year of the 90's, so the Red Sox have won 4 times as many titles as the Yankees in the 21st century.
It's a combination of a couple different factors:
Ownership willing to do what's necessary to win.
Good managers (other than Bobby Valentine).
Great free agent selections (Manny Ramirez, David Ortiz, Curt Schilling, Mike Lowell, Josh Beckett, JD Martinez, Chris Sale, David Price etc)
Good job drafting and developing their own young players (Dustin Pedroia, Mookie Betts, Jon Lester, Jonathan Papelbon, Kevin Youkilis, Jacoby Ellsbury, Xander Bogaerts, Jackie Bradley Jr, Andrew Binentendi etc.)
· 8 months ago