The only ones Bayern can blame are themselves, from board, through coach, but most of all the players. They were missing empty net and 1 on 1's. Neither Beckenbauer nor Van Gaal missed those chances. Bayern outplayed the merda in the opening 45 minutes from every point you look at it.
Then after the players fucked it up badly, it was Van Gaal's turn. His team backed up and didn't play the same tactics as in the first half. They started defending closer to their goal instead of pressing Inter in midfield. After that Robben was replaced (maybe there was a good reason for that, though. I don't know) and Bayern weren't the same in attack. A lucky goal out of nowhere put Inter back in the match and then it was almost over. Bayern's defense is very bad anyway (Lahm is the only good thing there) but when they decided to defend it was clear that the clowns will fuck something up. Breno gifted a ball to Coutinho (?) when he should have simply cleared it up.