By not signing Olise, the chavs may think they can escape a tapping up investigation.
I would expect Olise's new contract to have a release clause. It will doubtless be higher than the one in his now superceded contract, but I bet there's one in there because he held a lot of power in this situation.
Even if the chavs had to abandon their chase for fears of being done for tapping up., other PL clubs would have been prepared to sign him for £33 million. By signing a new contract, Olise has closed that door.