Not to mention that if you're looking for copyeditors on freelancer websites, you've got to provide them with some credit card details and evidence you are running something most freelancers are going to identify and report as criminal activity. There's a reason the majority of these scams want cash payment in Western Union or Bitcoin...

They are not THAT stupid. You need hear a native speaking for a couple seconds to notice that your English is not native-level

They don't do that because the promise of the scam is easy money. That means, low investment and high profit.

Imvesting time and money into proficiency level skills kinda defeats the point of working for a scam company.

At that point you'd rather find a legit job with a good salary for local standards

I was making a counterpoint that the reason they have bad grammar is not lack of access to a way to make good grammar. The original thought about why the grammar is always bad on scams is simple. The bad grammar is a litmus test that your victim is dumb or mentally not able to analyze your scam so you know to dig in when you get a hit.