This is exactly why.
The amount of price to performance does not scale well.
That doesn't make it horrible for gaming though, it just makes it too expensive to use. One could argue that if it weren't as expensive, it would be the ideal choice for gaming. It's like arguing that using LN2 cooling on a GPU for gaming is horrible. It's the best cooling performance you can get, but it's just not financially feasible to use. But if it were financially feasible, everyone would be using it.
However, there is the question of how much return you get for the better performance. Using two stacks of this for ~1Tbps of memory bandwidth isn't going to give you a 100% performance uplift because most games don't have that bad of a bottleneck when it comes to memory. There are certainly a few, and more bandwidth would definitely help if you can't achieve good compression for whatever reason, but just because something is "better" doesn't mean that it's that much better than some other "good enough" solution.
Any new technology always has this kind of ramp up where it's not widely used enough to reach the low prices provided by an economy of scale and because it isn't cheap enough or available in wide quantities there isn't a massive push to adopt it. If NVidia wanted to they could switch over to HBM for all of their cards, but is there enough global supply of HBM to meet NVidia's demands? Probably not, which means that even if they wanted to switch for performance reasons, they probably couldn't.
It would be better for the world if everyone switched over to using electric vehicles. Not just because it's better for the environment, but because they're more efficient and have better performance characteristics in many ways. They're a better vehicle. But we can't do that yet because they're too costly, and even if cost were no objective, there's simply not enough supply to move everyone over to using one even within the next decade. But no one is going to call them horrible cars because they're too expensive.