Grab has no employment contract with riders and vice versa. When they cut the incentives, existing riders have the right to walk away without any compensation.

It is not the same as working for a company bound by employment contract. If one day, the boss cut the salary down by 50% without notice, the employee can fight back in labour court.

Same case as Uber in US currently where the gomen is trying to prove that Uber drivers are employees of Uber Inc despite not have any contract. Still pending in court. If employees win, Uber is fucked.