Chelsea need to be much more active in the transfer market now. They even need to be the most active team among the top teams of the league. Because they have parted ways with many players in this transfer window. They will need to replace them with solid alternatives as soon as possible. They are in a rebuilding process in short.
Pochettino has a big responsibility to carry this team to the place where they need to be. Chelsea wouldn't target the league title for now of course. The first step will be to finish a season in top 4. They still need time to be able to fight for bigger goals after leaving a poor season behind.
Chelsea are active in the summer transfer market, not because they brought in several players, but they are doing laundry by selling their players. Maybe this was done because Chelsea wanted to get funds for club operations or it could be to buy players needed by the club. We know Pochettino definitely wants new players to suit him and he won't bring in players he feels aren't part of his strategy.
Now Chelsea have managed to sell some of these players, but so far only Nkunku has managed to join but that too because of the agreement that was made last winter with Leipzig. So for now Chelsea hasn't brought in any more players for the summer.