Also, I feel like a lot of fullstack JS is written by people who started with frontend JS and don't have nearly enough backend experience
The standards haven't changed; for the vast majority of JS programmers, this is their first programming language and they have no solid foundation of architecture and security.
So what you get are these overly enthusiastic newbies that want to share their latest achievement with the world (say, a function to left pad a string), and why not include a fancy post-install script with emojis that makes adoption even simpler for other complete noobs? And this is the result.
Educated or not, there are many programmers who simply don't give a fuck. Unless you make all the IT jobs a regulated profession and enforce significant yearly recertification, the mediocres will dominate. You cannot be nice and inclusive to mediocre programmers and expect good baselines.
This would merely optimise the industry for people who are good at wiggling through bureaucratic hurdles. It would entrench mediocrity while lopping off the extreme ends of the skill distribution - on both ends.
You're not wrong that there's a lot of crap, a massive legacy, and some bad behavior. It is also approachable, flexible, and portable. Even if you sometimes need to say "Wat?!?"