1. If these errors caused attacks to be unsuccessful then I expect (competent) attackers would stop making these mistakes
2. Plenty of real people make spelling errors or write single sentence paragraphs or even plagiarise things (or have their own descriptions plagiarised). Real people also host group things on personal sites. I think relying on this sort of thing is too likely to lead to false positives (and its a lot easier to spot the “signs” once one knows the email bad) and too unreliable in the long term for reason 1.
One thing I wonder is how this sort of thing might be prevented. It seems that once one’s pc is compromised there isn’t much one can do; newer security mechanisms like security keys don’t help much if the device is compromised. I don’t know how hardware bitcoin wallets (or similar devices) work so I can’t say whether they might have protected the targets of this attack, although I would guess they would not.
Sometimes I wonder if this is something there should be insurance for, but would anyone buy it? I think it would have to start as insurance for companies (which would require large numbers of companies to consider a breach like this a major financial risk) before people but such attacks would have to be unlikely enough to be successful for the insurance to be cheap. I suggest insurance with the vague hope that an insurer would want their customers to be more secure to decrease the chance they have to pay out. I don’t know if it would work that way in practice.