Because Chelsea did have a lot of players last season so when they want to rebuild their team it looks like there will be a lot of players to let go, Pochettino certainly has considerations that is why he prefers to accept offers from Chelsea when the season is over so he can use plenty of time to evaluate players who were at Chelsea prior to his arrival.
when Pochettino arrived as a new coach at Chelsea there were many changes in the reshuffle of Chelsea's players which maybe Pochettino's goal was to improve the team's performance which had weakened in the previous season and to buy several new, more reliable players to be able to improve Chelsea's performance. but here the problem is Pochettino is selling a lot of his players and some older players are also being sold as if they are too aggressive with their goals.
I'm worried that Pochettino will only make Chelsea's situation worse and I've always had doubts about whether Chelsea should really suffer in the next few seasons until they find the right coach.