prefer bool() threw an exception on receiving a string, rather than act the way it does now.

That breaks the truthiness cornerstone of the language. You can write

  a = 1 # or [], (), "yo", "false", 3.2, MyFooClass(), (1,), False
  if a:
    fire_ze_missles()
  else:
    declare_peace()

Upon encountering `a`, Python is evaluating bool(a). If that no longer works for strings, you now need a separate code path for determining a non-empty string.

It can short-circuit the brain upon reading a word that you know means false, but the Python rules are consistent. "Empty" is False, everything else is True.