I believe that would create alot of nasty confusion, and make localized globals all but useless inside of coroutines. For instance, the following would be quite troublesome:

sub my_iter {
  for (@_) {
    yield $_;
    # upon return, $_ may no longer be localized. if we
    # modify it, we could be modifying a global value
    # outside our scope. there's no way to tell, and 
    # that's rather nasty.
  }
}
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Of course, one could avoid using localized globals inside coroutines/generators in the first place, but where's the fun in that, I ask ;)

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print