Can't do LINE POWERED POTS over fibre. Not "can't do POTS."
Six of one, a half-dozen of the other. There's nothing "plain" or "old" about the equipment necessary to make any telephone work over fiber. And POTS does in fact include all of the necessary electrical power and signaling required for a POT to work with it. If an old western electric phone can't use it, it's not POTS.