I would imagine it might be the same with those ads.
This "just-so" story gets repeated constantly in threads about scams, but I've never seen anyone put up any actual proof. The more likely explanation is that scammers are just bad at English since they're predominantly from poor third-world countries.
It could be sloppiness, but I think scammers just organically copied efforts that worked, and those were the ones with poor presentations because they pre-filter and so target the scammers efforts more efficiently. The scammers need not be aware of why it works.
It is intentional. People who will not notice, are the least likely to complain later.
Do you know why all these “Nigerian prince” emails are of a very specific style?