There's a definite relationship between their music getting experimental and their decision to stop touring. Even on their last tour they couldn't even play anything from Revolver and had a hard enough time playing Day Tripper.
It's probably a chicken-and-egg thing as to whether they wanted to stop touring so they could make experimental music or they started getting more experimental because they were no longer touring, I can see it being a little of both. Primarily they wanted to stop touring because of the massive clusterf*** that was their final tour in the summer of 1966. They got roughed up by the Philippine army in July, then in August went to tour the US while John stupidly spouted off about Jesus, at the same time that race riots were breaking out in a lot of the cities they had to perform in (if their tour was a month or two earlier they probably wouldn't have had a bad time). Even if John and George wanted to stop, Paul still wanted to tour until late in that US tour when even he'd had enough of it.
The two other effects of the decision to stop performing live which probably shape their sound going forward were 1. Brian Epstein losing his influence over the group and 2. not having to get up to perform every night, their recreational substances of choice went from uppers to downers (especially John).
Don't forget the fact that they were nearly electrocuted on stage during a rain storm.
Would you classify acid as a downer?