How come John Lennons solo work sounds like a continuation of

Paul's solo material all sounds like Let It Be / Winding Road. Even John went on to say that they may as well have been Wings songs.

because george harrison can't be tied down to a single genre of music while lennon can only make simple pop music

At his best, Lennon actually embraced glam and funk very effectively; one of these days, people will finally appreciate Walls and Bridges for that. I don't know if I'd agree that Lennon's solo work is just a continuation of Let it Be.

George's solo stuff is unlike the Beatles primarily because of his spiritual sensibilities. Many of his best songs are catchy and perfectly musically engaging but ultimately lyric-centric and deeply influenced by Hinduism ("Simply Shady", "Crackerbox Palace", "Woman Don't You Cry for Me"). With a couple of exceptions, the Beatles were never an explicitly ideological or really very philosophical group. George individually wanted to write songs about his worldview and philosophy because he engaged with religion in a way that the other three Beatles did not, at least, not so publicly.