Who's to say how and why the dynamics of friendships evolve? I laugh when young girls talk about BFFs. They have no concept of life and relationships.
I'd posit that the members of The Band were closer than the Beatles ever were. They were basically living together for years on end between travelling with Ronnie Hawkins, then on their own and then sharing a house for a year or 2 (Big Pink). My understanding that it wasn't until moving to L.A. and the drug scene that things went downhill. They had great times together and always talked about them fondly, until the later years.
The Beatles lasted for about 8 years and the Band for about 7.