Suppliers don't just screw
Suppliers don't just screw over one customer in favor of another. The customers (which includes automakers) agree in advance buy up a certain amount of the chip production. And when the pandemic hit and vehicle sales went down, automakers reduced the amount of chips they were buying from the silicon manufacturers. Some gave up more than others in order to cut costs, which it seems like Subaru was one of those that gave up more. At the same time, computers and other home electronics went up in demand, so those companies bought up all of the chip supply that the automakers relinquished. Now, automakers want to make more vehicles, but the chips can't be made fast enough to supply everyone who wants them. Obviously, those that have them aren't going to give them up because they like making money. So that's what put Subaru in a tough spot at the moment. The only thing that will fix this is if demand goes down or silicon production goes up (but that takes years to get a new facility up and producing chips).