The reason they stopped touring in 65 was because they got sick of all the frenzy and trouble at their gigs. It became a nightmare. Harrison was still playing lead live when they quit touring. Lennon was a excellent guitarist, as is Macartney, but he wasn't interested in playing lead. Clapton took the lead on guitar weeps simply because he was a close friend of harriosn. No other reason I know of.
There's actually a gig front Toronto where Clapton is the lead with the plastic one band. It's not live peace in Toronto bit another gig. Clapton was so stoned he couldn't play and just stood there on stage. So Lennon took over and he was simply superb. I never knew he could play as well as that. I had a copy of the gig but I can't find it any more.