I'm going to try make it simple through an example..
Let's say PW was Zuma and he wanted his own Nkandla. His peers would have klapped him so hard he would still be spinning & the procurement chain would have refused to sign off the unauthorised expenditure.
So I say again, Zuma is not the problem..
First, the Nats were also corrupt. Maybe not to the same extent as the ANC, but definitely corrupt. You are looking at history with rose tinted glasses if you think that corruption would not have happened back then - it could and it did.
Second, if PW was Zuma, he would have made deals with the right people on the way up, promising them rewards in exchange for supporting him.
This is exactly what Zuma has done. Zuma has created a patronage network in which people loyal to him get rewarded and protected. Remember the Waterkloof air force base thing? Zuma protected the person who took the fall.
As long as Zuma is in power, there will be a lot of corruption because Zuma creates it. He has managed to get his network into power, and he ensures that corruption continues. Suppose that some of his cronies suddenly grew a conscience and decided to report Zuma to the authorities. Zuma has dirt on them that will ensure they go down too. Not only that, he controls the Hawks and the police. Who do you think is going to investigate the claims?
And I reiterate, this is all Zuma's doing. Zuma set this network up. Zuma removed the independence of the Hawks. Zuma corrupted the police. Zuma corrupted that idiot who investigated Gordhan. Zuma made the deals with the Guptas.
Yes, the ANC allowed this to happen. The ANC, even not counting Zuma, is definitely not innocent. But, Zuma is still the biggest reason why the government is as corrupt as it is.
You only need to look at the Thabo Mbeki government to see this. There was still ANC corruption back then, but not nearly on the same scale. The corrupt deals were not as big. When Zuma came to power, the game changed. Corruption went from being a hobby to a national pursuit.