As a long time JavaScript developer I honestly believe, and I really mean this, that maybe 4% of the people employed primarily doing JavaScript work actually know what they are doing. Just 4%.
It seems at the beginning many of the early Valve team had a lot of passion but almost no real experience in that kind of code or product. They got a massive springboard with the Quake code and then figured out the rest. They didn't stagnate on the Quake code, but wildly modified it to fit their needs. Most JavaScript people are not capable of this. They just stagnate at their favorite framework and then just spin around code style and process.
What differentiates that early Valve team from all these various JavaScript teams? It clearly isn't education or professional maturity.