I'm not sure it's the case with the type of scam that the article is talking about. Phishing credentials and getting people on the phone to buy gift cards and transfer money require a vastly different approach I suppose.
https://www.youtube.com/watch?v=18bovtIlrpI
Skip through the hot parts of the video per the graph and just see how the scam actually works, and I think that for all the social engineering steps required and the sheer amount of time spent on the phone, most people would just give up even if they maybe fell for the initial well designed email.
I don't really want to speculate on the spelling/email of scam emails as I think short of some reporter just finding a spam-house and asking, it will all be senseless speculation. The article theory has plausible theories, but might very well be specious. I don't buy that it's due to poor English skills, as spellchecks are plentiful and I have no doubt that the spam-houses could easily pirate older copies of Word and get a decent looking email.
Similarly, if it was effective, I have to imagine that this is the format they'd pick.
The simplest explanations of the poorly formatted/written emails and chats for me are:
1. The targets that have the highest chance of success don't care about the emails
2. The formatting of the initial emails doesn't impact the scam in a significant way
From a more personal perspective and the people I know who continued with the scam past its initial stages, they didn't pay attention to the formatting, just the general idea behind the message was more their concern. The IRS scams, giftcard scams, etc, put some sort of pressure on the people in a way that they truly stopped thinking about the content and were more worried about the idea behind the message: they would get in trouble if they didn't comply, and the financial concerns were the driving force.