RNG vulnerabilities are usually really bad in terms of the systems they compromise. It often means exposure of keys, huge numbers of jailbroken devices, or something similar. Making at most tens of thousands of dollars in Minecraft with one is sort of cute and fun in comparison.
Of course, I could be underestimating this by a lot.
One way of thinking about it is that each bit has maximal information because knowing the entire previous history should give you no information about what the next bit will be ahead of it being revealed.
Yeah, there is a big class of "RNG bugs" where someone uses a non-cryptographic RNG for secure things, not realizing that those things are supposed to be secure.
The classic example of these is a password manager that gave out recovery codes using a PRNG. This is in that class.
While a CSPRNG would have solved this problem, it also would've created a new one: much slower chunk loading and random item placement, which would have greatly slowed down the game simulation, and thus tanked framerate and playability. As it turns out, the right solution is to use multiple, isolated non-cryptographic random number generators with distinct state. That way, even though you can guess the state of one of them, it doesn't give you any insight into the others.
Modern CSPRNGs can generate numbers at GB/s, I find it hard to believe it would slow the game down in a measurable way.
The "right" solution you describe sounds overcomplicated and error-prone (now you need to think carefully about which domains are separated) compared to just using a CSPRNG.
The problem of dealing with randomness is about figuring out how to use CSPRNGs (and TRNGs) as little as possible, but not too little. CSPRNGs can get to a couple of GB/sec on a core, so they're not all that bad, but non-secure PRNGs are over an order of magnitude faster. I would assume that most of those things (eg chunk generation/loading) don't need secure RNG at all.
Sharding your RNGs by player is also an option for some games, and can be easier.
This is not little payout, it sounds to me like one of the most significant exploits in anarchy minecraft history, possibly even more than nocom.