We don't.
Legally, that good or cash continues to belong to the purchaser/owner.
I don't see how these two statements are compatible...
So I 'give' cash to my daughter, lets say $10,000.
Can she spend it? Does she own the things that are purchased?
If she places a bet at the casino and wins another $10,000 is that hers?
If the purchased goods/winnings do still belong to me, you are stopping me gifting to another person. So if you cannot transfer legal ownership of cash, how do you stop someone from doing this?
Am I allowed to sell my possessions? Could I not just sell my car to my child then give them the cash back? or never physically transfer the cash in the first place?
At what value can I no longer transfer ownership to another person? Does a family photo count? How about a commissioned painting of my family?
I honestly can't think of an answer to these questions that doesn't involve a ridiculously over the top authoritarian government. For many people, myself included, this would be far from utopia regardless of the outcome.
Yes, she can spend it.
No, those things are not hers, once she didn't buy them with her own money.
No, those $10K are not hers, once she didn't win them with her own money.
Yes, you cannot make a formal gift to another person, to anyone. That's the idea.
From doing what? Please explain.
Yes, you are allowed to sell your possessions.
No, you cannot give them the cash back. That's the idea.
It's them who need to make the transfer, not you. If they do not transfer the money, let's say $20K, they have $20K from nowhere. They could be charged with ilicit enrichment.
At anything greater than zero. Of course no one will charge a person that has 50 cents from nowhere with ilicit enrichment. But if it's about thousands or millions, you can bet it will happen.
Yes, a family photo counts, everything counts. If one relative of yours want it, he/she can buy it from you. That's the legal way. If you give it to him/her, no one will be arrested. It's like photocopies. It's illegal to photocopy books, even one single page. But, if you photocopy 1 page, nothing will happen to you. If you photocopy hundreds of books, I'm not sure.
You don't need an authoritarian State. You just need common sense. Like in the application of ilicit enrichment and copyrights infringement. Those restrictions already exist and you don't need a ridiculously over the top authoritarian State to enforce them.