If you have the resources to send thousands (if not millions) of these E-Mails, wouldn't you take 1 week to actually compose them rightly, hire a translater for a week or whatever?
In some cases, these are people with a strong distrust of "mainstream" communications, possibly assuming that anything written well or from certain sources carries an agenda that they don't want to be part of. In other cases, people may just be naive enough to believe that a company with a professional writer on staff wouldn't need their money and that therefore a company without a professional writer (which then writes with occasionally poor grammar and spelling) is more in need of support. In yet other situations, people may have become over-zealous in their support for social sensitivity and feel a strong urge to "help that poor boy in Nigeria."
There are probably a lot more reasons this works on certain people, and a lot more types of people that this works on.
So naturally, they also don't have the advantage of having better grammar and better spelling than us as well.
https://www.microsoft.com/en-us/research/wp-content/uploads/...