I think it's passion. Or at least redirected passion. I don't think U2 are any less passionate.
I think Pop shook them off the top of the mountain, at least mentally. I think the shift in passion then went from what the product was, to what the product does. They are damn passionate about staying on the top of that mountain. It's not about releasing something and hoping it reaches the goal, but starting at the goal and working backwards. That's where the passion is. The goal isn't soul anymore, no matter how much he tells you it is (and he never had the need to try and convince you of it before) the goal is the mountain top.
And you can hear it in the songs. The seriously restrained Edge as a start. Vertigo is a gimmick rock song done to a formula. It is exactly what has pretty much killed rock off, but that's another point for another thread. There is no passion in Edge's guitar, think of Bullet The Blue Sky. Think about the parts in songs where all the attention is on the Edge and Edge alone. The end of All Because Of You, or the end of Love & Peace. They don't launch and take off like he normally does, a solo that is a perfect continuation of the mood and lyric of the song, like it's the parts that Bono simply couldn't find the words for, so left it for Edge's guitar to describe. On this album they stay very restrained and have a feel of going through the motions. Is that a deliberate decision to reign Edge in, or is the passion not in the songs to begin with, leaving Edge nothing to naturally feed off and run with?
But particularly with Bono. The guy sounds like he's trying to write a passionate lyric deliberately, and he's not that great at it, which suggests to me that the emotion or feeling behind the songs isn't as real to him as in the past. He then sounds like he's trying to sing it to sound passionate, but that alone doesn't make it passionate. For example, there's a billion times more genuine passion in the quiet falsetto notes he holds in Running To Stand Still then there is when he yells "I've had enough of romantic love" in Miracle Drug. It's like he's thinking, "This must sound passionate" and the most obvious way for him to sound that way is to scream. If you're screaming, it must be something you are passionate about right? When it's not coming naturally, it doesn't work. You can see right through it, and Bono spends half the album screaming away at the top of his lungs. The brilliant way that One or Bad swirl around you and build naturally to a point that almost surprises you at the end is infinitely more believable then the forced building and rush to create an emotional moment that is evident in songs like Original of the Species and Miracle Drug. Both musically and vocally.
Meanwhile, get them in an interview and talking about the album and there's the real passion. It'll top the charts!!! It'll reclaim the radio for rock'n'roll!! We are the biggest band in the world!!! It's our best album!!! We don't want to leave this mountain top!!!! That's where the passion is, and that's where the fundamental change at the core of U2 has come from. That's what I'm talking about. The absolute need for chart success above all else has stripped away the very fundamentals that made U2 amazing in the first place. In the process of trying to stay at the top of the mountain, they are throwing away all the equipment they used to climb it with in the first place. The music is lightweight, shallow, forced, ie everything it used to be the exact opposite of.