The undeniable fact of the matter is that the overwhelming majority (based on my vast experience) of ESL writers in the "essay industry" employ broken English.
I do agree. However, you must take into account the fact that not all customers seeking help from writers and companies look for the finest quality of papers with regard to English language. In fact, there are many who precisely state that their language is not perfect, hence, the paper should also be similar to their writing levels.
Desperate writers who are located outside of the US are also much more likely to break US copyright laws and plagiarize.
Some companies do take strict measures to avoid plagiarism, and if a paper or an assignment is found to be plagiarized, the writer is penalized strictly.
Those who are dedicated to their jobs, know plagiarism to be an offense and thats the reason why many writers stick around for several years.
Having said that, it can't be denied that like in any other profession, there are people who function with the sole intention of making money, and would, in due course of time, run out of work, or, be fired.
Who gets the shaft? Consumers.
Consumers must be smart enough to thoroughly research before actually seeking academic help, a decision which could change the course of their future, with the help of forums, such as this one.