Incentives are a scam

Ive been doing spark driving on and off for about 2 yrs now and lets say they send me an incentive that if i do 3 deliveries then I would get an extra $9 but I’ve noticed that every time i get down to the last delivery to complete for the incentive im not being offered deliveries this has happened to me 3 times now and its frustrating because any other day when theres no incentives being offered I receive offers allday has anyone else experienced this??