That's not really a change at the language level. The language doesn't force you to do so, you can simply create an allocator as a global variable and avoid exp

That's not really a change at the language level. The language doesn't force you to do so, you can simply create an allocator as a global variable and avoid explicitly passing it around, which is basically what happens in every other language. The difference is instead social: everyone is onboard with the idea of explicitly passing allocators around.