1. Lots of extensions, which can control when they release the GIL unlike regular Python code, depend on it 2. Removing the GIL requires some sort of other mechanism to protect internal Python stuff 3. But for a long time, such a mechanism was resisted by th Python team because all attempts to remove the GIL either made single threaded code slower or were considered too complicated.
But, as far as I understand, the GIL does somewhere between nothing and very little to prevent races in pure Python code. And, my rough understanding, is that removing the GIL isn't expected to really impact pure Python code.
