The problem was they filmed the ending flashforwards in season 2 and didn't realize how things might evolve over 7 seasons. Once you get to season 9 it no longer makes sense for Robin and Ted to be together. They explain this to us multiple times a season and you can't spend a full season her wedding to Barney and then divorce them in 3 minutes in the next episode. They boxed themselves into a corner and refused to just toss out of the preplanned ending and just not do a flashforward at the end. Everyone loved Tracy. Just let your 3 married couples live happily ever after.