First, early versions of Go strictly required a “return” as the final statement in a function, rather than just checking that each branch terminated successfully (i.e. you couldn’t return from both branches of an if/else, you also needed a redundant return statement afterwards). So I think initially the compiler didn’t perform the kind of escape analysis that would make block-scoped “defer” easy to implement.

Second, block-scoped defer is really equivalent to RAII via constructors and destructors in C++. Go was specifically designed as an anti-C++, an attempt to return to the roots of C and improve on it, so the designers would have been very wary of copying C++ features like RAII.

I think it was a mis-step, and they should have gone with block-scoped. Other languages have copied Go’s syntax, but they’ve uniformly opted for C++’s semantics, which in this instance are much easier to reason about (definitely not always the case with C++!)