Not to be cynical but in modern day football, you never quite know what will happen.
Managers come and go, players change their minds and teams need different things – not to mention some pretty outrageous bids being made.
That all means that no player is at a club for life and by securing Oscar’s future contractually at least, should Chelsea want or need to sell him, they will make sure that a pretty penny goes their way.
Essentially, it is a smart bit of business from the club and their board.