I don't really understand the mentality of people who do this sort of criminal activity. If he'd stopped after, say, $5m and just retired he'd probably have managed to get away with it. Continuing to such a ridiculous degree through sheer greed led him to a death sentence. That's just plain stupid.

In for a penny, in for a pound. Unless you are extremely crafty, you don’t get to retire from this sort of criminality. Everyone who enabled you wants more and you have a semi-permanent metaphorical sword hanging over your head.

The culture of bribes is a bit different in China. 'Mutually assured corruption' describes the situation better.

People get away with this all the time—you just only hear about the stupid ones.

I think your logic makes sense, if this was both logical and about the money. But it seems to be more about greed, discontentment, and "more". There is no limit to "more".

It's the wielding of power which is intoxicating, the monetary amount just illustrates how many decisions he could personally influence.

Once you start high-profile criminal activity you have to keep doing it to pay off the right people, as soon as you retire you're fucked.

It's called greed, as you aptly pointed out.

This kind of crime means you develop a network around you that won't stop having expectations of you just because you think you have enough for your eventual retirement.

They'll basically be your friends, partners and coworkers. Making a sudden change in how you associate with each other can have rather negative consequences, ranging from anxiety to them trying to murder you.

This is load bearing guanxi

Think of Breaking Bad. His wife literally asked him this same question. When is it enough?

It's a mentality where you can't stop.