You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
Or you just bias the power vacuum to be filled with even more paranoid and ruthless nutjobs, because the more sensible psychopaths choose to avoid the consequences you are proposing. We see this fairly consistently when authoritarian governments get coup’d - the person most likely to take the place of a bloodthirsty dictator who knows he could get assassinated at any moment is an even more bloodthirsty future dictator.
When authoritarian governments get coup’d and there is external influence seeking to further destabilize. Also every authoritarian dictator needs a class of people loyal to the regime, who fall into the category of people wanting power but also staying alive.
We also see many dictators that got more paranoid over time as they ruled too long, because there was no opposition to keep them in check until things exploded fully.