Your first line says SO much of what's wrong with the web as a whole. Generally speaking most all computer technology is built on the model of "three years is obsolete, five years is the scrap heap" and yet SO many people have their craniums permanently wedged up 1997's rectum.
"Web rot" being a prime contributor to that; old outdated outmoded tutorials, old outdated outmoded threads, and sites that don't do a damned thing about it trying to coast on basically reputation and nothing else. StackOverflow DEFINITELY suffers from this, as do places like W3Fools. This broken twenty year out of date mindset then seeps into other projects -- see mind-numbing asshattery like bootcrap, or worse w3.css -- but because they can slap the HTML 5 banner around it everyone toots their own horn over how 'modern' they are... as they ignore semantic markup, separation of presentation from content, logical document structure, graceful degradation, and accessibility minimums.
It's one of the biggest problems with the web, old answers tend to stay up forever and people continue to blindly copy them. That's why after a DECADE of being told to stop using PHP's mysql_ functions, six years of giant red warning boxes on php.net, nearly three years of PHP 5.x throwing warnings, and a good year and a half of it flat out not existing in PHP 7, we STILL have people derping along building new systems with them or refusing to update their software to even run... and the folks forced to run around like the sky is falling when AGAIN we've been basically told for a DECADE this was coming!!!
In that way, StackOverflow's "there is only one best unchanging answer" is almost as stupid as the inflexibility of radicalized faiths. It would almost feel like the place was unmoderated if not for the heavy-hand they show about EVERYTHING else.
But it could be worse, remember ExpertsExchange in all its "wait, this is a tech site not a gender re-assignment one" glory where 90% of your Google Searches for ANYTHING technical pointed you at their huffing paywall? Can't say I miss that one damned bit. Now there was a site steeped in black-hat SEO bull that NEEDED to be killed with fire. Could never figure out which was scarier, how EVERY search engine shoved that stupid blasted site in our faces, or how there were people dumb enough to pay for memberships there!