No doubt some treaties are bad treaties, in that they make the world a worse place. But whether a treaty is good or bad and whether it is legally valid or invalid are two separate questions.
The problem with "questioning transactions" is that if you happen to own any real estate, almost certainly it is land which was stolen from somebody at some point (from indigenous people, or by some invading army, or by some greedy feudal warlord, or whatever). You want to open that can of worms for other people, but do you want to open it for yourself?
Oh my. I just looked, and it turns out in the US there is apparently no such thing as voiding a sale due to it being forced, only 'fraud' understood as misrepresenting the value of the property or the origins of the money haha
So, here's the issue. In other countries, especially over here in South America, this kinds of transactions are heavily frowned upon, and criminal acts resulting in a sale are regularly cited as reasons for voiding some sale or another. This is a bit of a worldview issue, we're not used to thinking about inflicting misery on others as a legit business strategy.
I'm not in the US, I'm in Australia. My wife & I, we own a house. If you trace back the legal chain of title, eventually it originates in a land grant issued by the colonial Governor of New South Wales in the name of the British monarch – and the British monarch's claim of ownership is based on Captain James Cook claiming the east coast of Australia in 1770 in the name of King George III. But, it wasn't unoccupied land – the indigenous peoples lived here, and they saw the land as theirs. In some other places (such as New Zealand or parts of North America), the British negotiated treaties with the indigenous inhabitants to acquire land from them – the fairness of those treaties is often contested, and the British having acquired the land often ignored and violated the other provisions of the treaty – but, in Australia, there were never any treaties with the indigenous peoples, the British saw them as too uncivilised for that, the British Empire just moved in and took over. So, if legal title based on theft is invalid, and our own legal title ultimately originates in the British Empire's theft of land from the indigenous – does it follow that my wife & I don't actually own this house (or at least not the land it is built on), even though we've paid several hundred thousand dollars for it?
Wherever you are in South America, isn't it the same story? The Europeans (the Spanish or Portuguese or whoever) moved in, stole the land from the indigenous peoples, then divided it up and gave or sold it to European colonists, and it has been on-sold and repeatedly subdivided since – so if land titles founded on theft are invalid, land titles where you are must be just as invalid as those over here.
Different legal systems codify different mores differently.
In Argentina and Chile, mapuche people to this day continue to legally challenge the ownership of land that they claim is theirs even after hundreds of years of having lost it to the genocide of their people -and dozens of others- as part of the creation of our nations.
In Uruguay, where I now live, this is very rarely still the case, mostly because the people who would have a right to challenge those lands ownership were very thoroughly murdered and their descendents have long been stripped of that right.
We're just not ok with brutalizing people as a business strategy. Like I said, it's a cultural thing.
The problem with "questioning transactions" is that if you happen to own any real estate, almost certainly it is land which was stolen from somebody at some point (from indigenous people, or by some invading army, or by some greedy feudal warlord, or whatever). You want to open that can of worms for other people, but do you want to open it for yourself?