I wouldn't call murloc decks face decks anyway. Not every aggro deck is a face deck. Face decks are all about delivering damage directly from hand to your opponent's face. You don't plan to maintain board control, and any minions you run should be able to deliver face damage even if you don't control the board, or at least be OP and low-cost enough that it doesn't matter. That's why Leper Gnome is a staple of face decks, for example, because it nearly guarantees at least 2 damage to face.
Murloc decks are typically structured more like zoo decks. They aim to spam minions onto the board and maintain board control, hitting face with leftover minions. They don't have means to deliver significant damage directly from hand without board control.
Murloc decks are bad because, unlike zoo decks these days, their minions aren't sticky and are individually weak. Murlocs are highly vulnerable to common early removal and board control tools, like Zombie Chow and Frostbolt, as well as most AOE. Being dependent on board control to win _and_ being bad at holding board control is a bad combination. If you're having trouble against murloc decks, it's probably a sign that your deck has weak early game.
(None of this applies to Anyfin decks, which are typically combo decks, not aggro decks.)