All of a sudden? They've been moving those two together since Season 3. I can see you not wanting them together, but to argue it was done haphazardly and at the last minute doesn't seem to jive with the history of the show, which has always posited that these two are the male/female equivalents of one another.
I could argue for days that you couldnt be more wrong. The show has evolved Barney in a way that makes him getting together with Robin, completely against everything that he has done up to this poit in the show.
When Barney and Robin first got together it was purely a fling and it was based on sex. As soon as it moved past that, they realized how terrible they were together sp they broke up. Past that point the only time Barney has ever "wanted" Robin was because someone else was with her and he couldnt have her (this shows his immaturity). Examples of this are when Robin got serious with the news anchor and when Ted and Robin started hooking up to stop fighting (Barney threw TVs and everything about this)
Then later Barney finally starts to grow up and move on from Robin when he dates Nora. Shes awesome and he likes everything about her and wants hmeverything he thought he didnt want before (kids, marriage etc). This is where he develops past just a womanizer to someone you can tell wants more than that. After all that Barney sleeps with Robin again and now has a want for Robin again. At this point he breaks up with a great girl that loved him to be with Robin, and what does she do? Tell him she cant break up with Kumar, which she has no real feelings for.
Here is his breaking point. Thats his closure for Robin. He broke his heart with making him break Noras. At this point, he is completely over her. He realizes in his head that they are too similar in some ways and too different in others (wanting kids). He has grown past what should be a phase (Robin). He has matured and is now really looking to settle down. This is proven to me when something was going on with Robin (i think when Ted told her he loved her for the billionth time) and he asks Barney how he feels about it, and Barney says with a straight face in complete truth that "I really dont care, dont have feeling for her." Now this is the same Barney that had shown no ability over 8 seasons to hide his emotions. That means he truely felt that way imo.
So now you have last seasons finally where Barney finally decides he wants to marry Quinn because shes perfect for him. He spends 29 minutes of the show proposing and growing truely past the point of being a manwhore. He has settled down, he has come full circle from where he was after he and Robin broke up. He is a mature person now....OHH WAIT NOW ALL OF A SUDDEN ROBIN AND BARNEY ARE AT THE WEDDING ABOUT TO GET MARRIED. Whattt??? Why couldnt you do that 3 seasons ago?? Whats the point of all that growth of Barney if hes just going to go back to a girl that has broke his heart countless times, wants completely different things in life and have shown to be terrible together.
They made the last couple season pointless. And if Ted cant be with Robin because they want differwnt things, then why is that not the same reasoning for Barney??