Things I don't understand: Lego Rock Band Blur

Here it is, proof that I. am. an. old. Get off my lawn! O.K, so WTF is Lego Rock Band? Why does it exist? It seems totally random. Take a popular children's toy and cross it with a popular video game? What about My Little Pony Halo? Or Grand Theft Thomas The Tank Engine (okay, that one actually might be all kinds of awesome.)
The best thing about this is that they captured Alex' innocent uber-smile so well, why is he always so happy? Damon looks like Eddie Izzard and Graham is Harry Potter. Dave's hair? Not so much.
[Youtube]