Playing GTA:O is not rewarding. You need about 500k to upgrade a car and a few weapons. You earn 500k in about 12 hours gametime. I'm not gonna spend 12 hours grinding the same mission over and over just to upgrade a fucking car.
And the missions aren't all that fun anyways. They're fun to play two or three back to back but then it gets kinda boring, more like a chore. It's fun to bullshit, chase after people, kill them, blow up their cars, get into copfights (the cops aimbot still sucks btw, they're snipers with shotguns), have dogfights, go on a rampage and other free roam stuff. But ALL of that costs a lot of money, and there is no fun way to earn much cash.
GTA Online is broken and all the bad sports stuff and taking away the money isn't making this game any better.
People are still gonna play missions if they have lots of money if the missions are actually fun.