Unpopular opinion, I think Damn is better than To Pimp a Butterfly.
But why?
First, most people say there is no theme. I disagree entirely. I believe it is Keirkagaard, or perhaps Camus levels of lamenting. He's having a serious existential crisis between the grey morality he knew in Compton, that he continues to see in the world, with the simple uplifting message of TPAB. The Fox response to TPAB brought back some anger inside of him he had forgotten since he's been more prosperous, and I think that put him back in line with his inner childhood demons that he exorcised on GKMC. He at times in this album admits to feeling like a hypocrite on TPAB, that he may actually be disconnected from the black community he claims to want to save. That he isn't a savior, and that his messiah complex can't be left unchecked. That he's just a rapper, a man, a musician, struggling with his life.
In XXX he says "I would chip a n-, throw the blower in his lap, and walk myself to court like bitch I did that." Then in Duckworth he takes a personal scenario and compares it to the age old existential question of, "How do you know what the right choice is, if the true results won't be revealed for years to come?" As in, 20 years later sitting in the record studio, all three of the making millions. Kendrick is trying to say, "I'm not a genius, I'm just lucky, like everyone else." It's very existential throughout the whole album, and explores religion, absurdism, hedonism, etc.
Then, the simple songs that people are complaining about like LOYALTY, LOVE, LUST. He made songs that by and large, the actual black communities will listen to. It's a reminder that he isn't making albums for hiphopheads, or pitchfork, or a grammy, or money. He's doing it for Compton and the black community of America at large.
Edit: DAMN is also as fun to listen to as GKMC, where as TPAB is offputting at times, and not a daily listen. I could bump GKMC and DAMN back to back every morning for the next five years.