As far as I’m aware the justification is “no executing pages you can write to at runtime” (because it’s a huge security issue). They give safari an exception to

As far as I’m aware the justification is “no executing pages you can write to at runtime” (because it’s a huge security issue). They give safari an exception to that because you can’t make a JIT without doing that, and that’s the most straightforward way to get fast JavaScript.