I will try and give this a go.
Despite his form totally falling off a cliff the past few months(since the beginning of march) and him in effect losing his starting spot. Prior to that he was pretty much a mainstay in the team, was a consistent feature of the 21 game-winning run the team went on, scored some important goals in the earlier part of the season 3 of which being match-winners in 1-0 wins and was a factor of why the league was pretty much won by the beginning of march before his form dropped. No amount of revisionist history will remove the fact that he started and played a part in wins against liverpool, spurs, everton and arsenal in a row which effectively sealed the title.
So here you have a player whom despite being in his worst form the past few months, will still end the season having the 3rd most minutes of all outfield players(excluding ederson), currently joint 3rd for goals with 14 and 2nd in assists with 11. Clearly this is a player who has been of some value to the team this season despite his loss off form towards the end of it.
Maybe pep has lost trust in starting him in the most important games currently but certainly hasn't lost complete faith in him as a player seeing he started him in the league cup final. If I was to guess, Pep and the management view this season and the false 9 as an anomaly and something that can't be sustained long-term going forward especially with the highest goal-scorer being a central midfielder with 17. Hence the seemingly huge priority of the signing of a top class striker in the summer. If that is to be the case he would probably feel having a focal point to lead the line would be what will help get sterling back into form and performing to the standards he has the past few seasons.
Thankfully this is a manager who doesn't base a player's overall quality or potential contribution on a few months of poor form because if he were to listen to many here, the likes of gundogan, stones, mahrez and even bernardo would all be sold by now.