In AL, clerics must select a domain from their deity's list, or the Life domain. Life domain is open to everyone (which is important for deities that don't have listed domains, or whose only domain is Death which is not available to most players).
The ALPG is sadly not as clear as it can be in this regard, but previous admin comments makes it clear that this is the intention.
Another reason to allow a global Life domain option: the Life domain is the only domain detailed in the Player's Basic Rules. As such, a player who hasn't (yet) spent any money on the game can still make an AL-legal cleric of any deity.