To be fair to Keita, he did start 19 out of 51 games across the PL and CL last year. With Thiago and Henderson fit for the bulk of the season, he did his job as a squad player and started in the CL opener against AC Milan, both legs of the QF against Benfica, the 2nd leg of the SF against Villarreal, and he was warming up in case Thiago couldn't start the final against Real Madrid. He also started the LC final against Chelsea and the FA Cup SF against Man City, and not to mention starts away in PL against Man Utd and Spurs.
Ox on the other hand has just lost his way and this team has evolved past his talents.
Hopefully they'll both return to training later this month and be able to start the LC game against Derby in early November.