Is anyone asking Nvidia to take back stock? And if so, what are the conditions under which this is being asked? If said stock was purchased through a promise of some future development that has since not come to pass, asking this is absolutely not unreasonable. Large scale business deals are rarely this cut-and-dried.
And, crucially, you're entirely ignoring the power dynamics in play here. Nvidia is the only company involved in these transactions with the economic power to hold any kind of buffer stock of products - AIB partners don't have the scale or margins to do so, which also makes it unreasonable for Nvidia to push that responsibility onto them. If one wants fair business practices, it is then entirely reasonable for Nvidia to bear the burden of holding such stock and setting up a system for dynamically allocating stock to AIB partners as needed. Such deals can still include long-term purchase agreements, they just need some built-in flexibility. Nvidia's deals with chip fab owners are an excellent example of this: Nvidia agrees to buy a certain amount of wafers over a certain time period - with some flexibility, but not a lot. But crucially, they have a lot of freedom in deciding on the fly what those wafers will be made into, despite this being far from trivial to implement in practice. What we're seeing inklings of here is Nvidia not giving the same type of flexibility to their downstream partners as they themselves enjoy from their upstream partners - instead passing the buck downwards to (strongly implied: replaceable) "partners" who are thus forced to bear the burden of risk rather than the much more financially stable Nvidia.
The core point here being: you're arguing from an explicitly naïve perspective that seems utterly blind to power and its implications and consequences - a blindness that's endemic to people espousing the virtues of "free markets", and the same blindness that renders these people fundamentally unable to see why said markets aren't free at all. Ignoring power relations in business doesn't get you closer to any kind of truth or justice or freedom, it just makes you blind to the realities of the world, and thus makes your analyses of how the world works deeply flawed.
The facts of the matter are these: without Nvidia, AIB partners have no GPUs to sell, and without Nvidia, Samsung has real trouble selling all their wafers (or at least has to take the increased cost of managing hundreds of smaller scale customers rather than one major one, if they are able to sell them and don't have to scale back production). Nvidia doesn't have all the power - they're still reliant on both chip supply, other components, and AIB partners for selling their products - but they have significant advantages in both relations (when the chip supplier is TSMC you could argue that they're pretty evenly matched on that side, as TSMC has no trouble selling every wafer they can make, unlike Samsung). And, crucially, Nvidia is widely documented to use this power for all it's worth, having no scruples about going into outright anticompetitive practices if they see the opportunity to gain from this. This isn't saying that AMD would necessarily be better if the tables were turned, but we literally can't know that, so such speculation is nothing more than meaningless equivocation - the fact of the matter is, Nvidia is a market juggernaut that loves to throw their weight around at the cost of their business "partners" for the sole purpose of enriching themselves and their shareholders.
