Why are there so many typos in phishing emails?

Is it really just that their English is bad? Why aren't there any intelligent phishers?
There are a couple of reasons why phishing emails often contain spelling and grammar mistakes. First, attempts to get past spam filters and messages being written by someone who is not a native english speaker are the main causes of the mistakes [1, 2]. Second, these mistakes are not really mistakes at all, but rather intentionally included by design [2]. The goal of a scammer is to make money, so they want to weed out responses from people who will ultimately fall prey to the scam and send money to them, wasting their time [2]. Incorrect spelling and grammar helps confuse or disappoint people who would use these red flags to dismiss the emails [1, 2]. Additionally, criminals prefer to send out imperfectly-written emails that reach their targets rather than perfectly-written emails that never reach their would-be victims [2].    
The intention behind many of the so-called "errors" in phishing emails is to intentionally mislead and discourage responses from anyone who is not sufficiently gullible to fall for the scam. [1] For example, the word "to" may be used instead of "too" to make the sentence seem more colloquial and perhaps more grammatically correct to English speakers. [1] Keywords and phrases that are commonly found in phishing emails are often misspelled to attempt to get around spam filters. [2] However, some of the errors in phishing emails are the result of the scammers having a poor command of the English language. [1]