That was kind-of the point of them originally, though - it didn't matter what the source was originally, because Artificers were tinkering with magic on a more fundamental level, producing the same effect without necessarily using the same cause.
What is Arcane magic, in your opinion? How would you separate what Wizards and Sorcerers and Warlocks and Bards do from what Artificers do?
WotC seems to have the idea that it's tinkering with magic on a more fundamental level - accessing the ambient magic of the cosmos and multiverse.
Or another way to say this, how is the Artificers tinkering with magic on a fundamental level differ from Bards accessing the fundamental underlying weave of magic via words and pitches and rhythms of creation?
If Divine Soul Sorcerers and Celestial Warlocks access Divine Magic, and an Oath of the Ancients Paladin can access Primal Magic, what makes why wouldn't that variability for Artificers just be something that varies with subclass too?