Maybe Chelsea saw something that we can't see at the moment. What I know is that Nicolas Jackson looks like an ordinary striker and his overall performance still far from being satisfactory. It seems like Chelsea still really hopes for the potential they think Jackson has. He probably has that because he's still young, but it could also be that he has reached a dead end, so that no matter how long it takes, he will still be like that.
If I was the coach of Chelsea Nicolas Jackson would been kept on the bench for most of the games. He has been a very wasteful striker who rarely maximizes goalscoring chances. But he is strong, a team player and humble, maybe this might be the quality the coach wants. As a striker, the goals should be the main objective. The reason why the club might give him this long-term contract might be because they believe he would improve and his earnings might be low. I hope the Senegalese will be able to prove to Enzo Maresca that he deserves this trust.