from the trailer "Get Back" by Peter Jackson, they were still a tight band. In the workplace it was all about the music. They appear at the end to LOVE each other when the tools of the trade were in their hands.

my guess is they had spent the best part of 10 years getting to be the best, nothing left to do or prove.

at age 30 Lennon & Ringo were getting old, McCartney thinking it was "his band" the others weren't buying it.

they were all rich & famous, done the drugs, the partying ... my guess is they wanted to retire - an excuse finger pointing to see who would say it first.

the young lad Harrison had a few more years.

the outcome ...individually they were successful.