The issue is that it's a slippery slope. When you start taking human rights away from one group of people, it could very easily lead to innocent people, or entire groups, being framed and legally stripped of their possessions. That's why I think opening that can of worms is a bad idea.

And it's not that easy. People figured hundreds of ways to hide wealth and there's no way you can regulate them all. Split it between relatives, buy non-quantifiable assets, hell they could buy bitcoins with multiple proxies on the dark web from an old pc in the middle of Africa and we'd know absolutely nothing of that. Unless you build some sort of utopic database which documents every living person's possessions and the exchange between them, it's just not possible.