Why doesn't threading.join() return a value?

[Roy Smith]

I have a function I want to run in a thread and return a value.  It
seems like the most obvious way to do this is to have my target
function return the value, the Thread object stash that someplace, and
return it as the return value for join().

Yes, I know there's other ways for a thread to return values (pass the
target a queue, for example), but making the return value of the
target function available would have been the most convenient.  I'm
curious why threading wasn't implemented this way.