Thread local storage means all async tasks (goroutines) must run in the same thread. This isn't how tasks are actually scheduled. A request can fan out, or contention can move parts of the computation between threads, which is why context exists.

Furthermore in Go threads are spun up at process start, not at request time, so thread-local has a leak risk or cleanup cost. Contexts are all releasable after their processing ends.

I've grown to be a huge fan of Go for servers and context is one reason. That said, I agree with a lot of the critique and would love to see an in-language solution, but thread-local ain't it.