To me the most important reason that you can't be forced to disclose a password is that it is impossible to prove that you know it at all. So you can always say "I don't know it" or "I forgot it" so these constitutional rights are basically ensuing you won't get tortured/harassed for something you couldn't reveal.

However with fingerprints you can "prove" that you can't unlock the phone by touching all the fingers to it so the problem doesn't apply.

Basicly there is nothing special about encrypted data, only the "data" inside your head.