Why are Nigerian letters so badly written?

Whilst half my emails are seemingly going missing, the Nigerian letters still somehow manage to get through:

What I don't understand is why they are so badly written. A 'citizen of Wales presently in England'? The nationalists haven't quite got their way yet. And why would such a 'citizen' have an email address with a Hong Kong top-level domain name? Surely there is a need for a site explaining how to create a plausible Nigerian letter.