JP and some others might come down on me for this, but....
Speaking as a former TH freelance editor, there are a few reasons for the mistakes readers often find here, including those which some would deem glaringly obvious.
Firstly, there's the pay - paying someone a penny-per-word does not serve to inspire heavy investment into actually editing the body of work being presented. I used to edit Wolfgang's articles and had to force myself to stop correcting mistakes outside of roughly an hour of time invested. Otherwise, it wasn't worth the money. Remember: one-thousand words only paid ten bucks.
Secondly, editors were (and likely still are) not responsible for any fact-checking whatsoever. So, all names, places, dates, times, etc. were solely the responsibility of the author. This essentially translates into the assigned editor ignoring such things.
These first two factors form a combination that essentially turns a person with the term editor in his title into little more than a basic proofreader. As an example, Activision was misspelled as or replaced with the word Activation within one of these tiles. To me, that's a clear sign someone, either the author or editor, used auto-complete or auto-correct, respectively.
Thirdly, there was no education requirement to become a TH editor. I'm a college drop-out who never scored higher than 500 on the Verbal portion of the SAT, yet I still possess enough basic English grammar mastery to be a TH editor, to the extent that TH's former Editor-in-Chief, Chris Angelini, once asked me to share the feature story editing load. I respectfully declined.