I’m sorry–you’re right that I should have spoken more courteously.
“Allah” does not mean “a deity in the general sense.” “Allah” means “the true God.” So when Muslims say “there is no god but Allah” they mean “there is no deity except the One True God.”
So it would make no sense to say “there’s no Allah except Allah.” “Allah” is not a word that Muslims would use for “a god”–a being people worship, including false gods as well as the true God. “Allah” is the word Muslims use for the One True God.
They certainly could say “there’s no g/God but God.” And many of them do. But Muslims, like members of many other religious traditions, tend to be linguistically conservative when using sacred terms. Bear in mind that they don’t think the Qur’an can, strictly speaking, be translated. Arabic is a sacred language for them so they tend to use Arabic terms when speaking of sacred things.
Edwin