Most of it is, because most of it is cargo-culting by amateurs who just believe what they read on SO and forums and who have never actually written anything non-trivial, much less shipped a game.

Are you saying they misunderstand what they're cargo-culting or are you saying amateur game scripts run fast enough? To cargo-cult it needs to be relevant somewhere, so either way it shows the blanket statement is false, no?

I'm saying most amateur games do run fast enough, and that for those which don't, the bottleneck is more likely to be related to poor caching, unnecessary allocations or unoptimized assets, etc, rather than just the language used. You really have to go out of your way nowadays to actually slow a game down with just bad code.

And many of the idioms people abide by may no longer be relevant, or may only be relevant in niche but not general cases.