Leatherhead
Possibly a Idiot.
Quote from Jeremy Crawford: Subtle Spell is meant to protect a spell w/o material components from counterspell, since you can't see the casting.
Right, So:
Spell components are used for the purposes of tracing spells back to their caster, and determining what can be Counterspelled; If there are no components to the spell, or if you cannot perceive the components, you cannot Counterspell. And indeed you cannot trace a spell back to it's caster (assuming you can otherwise pinpoint said caster in the situations that would obstruct your senses).
From that we can infer; Spells with only a Verbal component must be detectable through their Verbal component.
Which in turn means that Verbal components must be detectible in a standard combat encounter, which assumes a fight of some kind, to at least a range of 60' (the range of Counterspell).
And that's the entire argument. Verbal components must be significantly audible (to at least this exact metric of 60') in order to facilitate gameplay via counterplay.