I think this is right but it's also a little weird. I have the same question with Jones a little as well. Or at least the concern. Sometimes we do need our 8s to bring more to break down a low block but some of Keita's attacking dynamism seems to have been coached out of him. And given we paid a huge premium on Keita because he was elite defensively AND offensively (rather than just defensively) it does make you wonder why we even signed him in the first place.
The answer is not that hard to see. Things change and the best coaches have flexibility, know a good thing when it happens and build upon it. Keita was bought before the current power midfield had properly established itself. He was almost certainly bought to provide that vertical movement and thrust and dribbling and all those things he was known for, in what would have been a different midfield deployment than the one we have since habitually used.
Remember our first interest in him was before Coutinho left, and we tried (unsuccessfully) to bring forward his move immediately after Coutinho's January transfer in order to plug that gap. He was intended to be the improvement upon Coutinho: forward minded, creative but also tactically more disciplined and useful in the press and the breaking of play.
Unfortunately for him, but maybe fortunately for us as it has turned out, he got injured shortly after arriving and that's when the power midfield really established itself, along with Trent and Robbo being far more influential in the attack than anyone had anticipated. And that's why Keita found it harder to break back in even when he was fit again, and why he has had to bide his time. The very style of our play had changed. It worked and Klopp stuck with it.
These things happen. The good news for him is that with Gini gone there are now some hints that Klopp wants to tweak the midfiled deployment again (hence the unexpected promtion of Harvey to a starting spot). All being well Keita will get more games now, in the Gini role and maybe in a more attacking role in certain games.