http://www.mcvuk.com/news/39103/MTV-expected-more-from-Rock-Band-in-Europe

To sum it up, they think there were many circumstances that made the game sale worse. They think that, apart from weak economical momentum, Guitar Hero managed to capture peoples attention. They also think that won't be an issue for Rock Band Green Day.

IMHO, sales are really poor, specially if you take into account how low the sales have been for the country where The Beatles come from...

Do they really want to know why the sales were bad?

Because just about everyone is fed up of all these music games, seriously, they're selling worse and worse, and to be honest, I sort of blame Activision, because they're milking Guitar Hero, making people see Rockband as "Just another game like Guitar Hero", so people are avoiding it like the plague...

Seriously, if they didn't release them so often, maybe added more tracks on the disc, and give a better selection of songs, people might actually buy them... I've had to wait a whole year for DLC on Rockband 2 for a song I like... one WHOLE year for them to release a song I'd actually consider buying...

Very very poor sales, imo... the license must have costed a fortune!

Well at least this is a game that will continue to sell.

I do believe the reason is what you exposed in your first paragraph. I don't think it is the only reason, because another main point to consider regarding "RB The Beatles" is target group of age. Everything I could say about it is obvious.

I agree.  Its Activision's m.o. and it makes them a ton of money on the short term, but its not sustainable.

Personally, I don't see the broad appeal of a single band game, even if it is the Beatles. 

I just played through the entire game for the second time a few days ago. I got 97% on the guitar solo from "The End" and it drove me mad. A greater music game probably won't happen for years, unless somebody pulls their head out of their ass and makes one for David Bowie, spanning 5 decades instead of 1.

The only thing that hurt the sales is the release of 7 Guitar/Band/DJ Heroes last year by Activision. They've gone nuts.