They don't play it because Axl can't sing it. He's out of breath singing the first verse to jungle and that?s the first song they play. If they were to play Estranged he'd have to bring his oxygen tent on stage with him. As far as the band I think Fink would butcher the song he maybe one of the worst guitar players I ever heard. How some of you love this guy is beyond me. He's awful.
Axl seems to have distanced himself from the Illusion songs. Probably because of the complex nature of those songs and the inability of being able to teach the new band what exactly Slash was playing in those songs. Slash was all about playing with feeling and I think only Richard has some of that. You can't teach feeling and judging by the boots you can't imitate it either.
Estranged is not all that difficult to sing, relative to some of the songs on the current setlist. I would argue that WTTJ is tougher, for example.