Why didn't John play on George's later songs?

[Applejam101]

In 1969, the only George song that he didn’t participate in was Here Comes The Sun and that was because he had a car accident.
In 1968, John played on While My Guitar Gently Weeps and Not Guilty. He sang on Piggies. And he sang on The Inner Light.
In 1967, John Played on It’s All Too Much and Only a Northern Song. And sang on Blue Jay Way.

My point is John was participating in George’s songs in the late sixties. Yeah, he may have only contributed vocals on some, it may just be that John didn’t have a role to play.

[Lord Reith]

Don't forget that both John and George are sometimes barely on some of macca's late 60s extravaganzas. They might get to rattle a tambourine or sing a harmony if they're lucky.

I think John was less sure of what he wanted, or at least how to achieve it, so was happy for everybody to chip in and play whatever they wanted. Paul already had everything worked out in advance and handed out parts. George was probably somewhere in between as usual. A lot of his songs with the Beatles sound like they were recorded very hurriedly and without any serious consideration by John and Paul. This seemed to change around 1968 where he became more prolific and probably fed up with no-one taking him seriously.