One common criticism of cosmological arguments is that, even if successful, they do not establish the existence of a single creator. It remains possible that there be multiple beings one of which created, or that creation be the joint effort of multiple beings. Thus cosmological arguments for the existence of a monotheistic God are failures.
Typical replies appeal to Ockham’s Razor: in the absence of reasons for postulating more, we’re justified in thinking cosmological arguments establish the existence of just one being because just one is sufficient for the task. Here’s another reply, sketched in a rough and intuitive way, the theist might make. As far as I can tell, it will only work (if it works) for cosmological arguments that establish creatio ex nihilo, such as the kalam.
Creatio ex nihilo implies the creator be omnipotent. The ‘distance’ between existence and non-existence is ‘infinite,’ so to speak, and only a being of infinite power could traverse it. Some have argued that there is no greater difference than that between the abstract and the concrete. But it seems more plausible that there is no greater difference than that between existence and non-existence. Any being that has such difference-making power has power none greater than which can be conceived. This is little more than an intuition pump, but it pumps my intuitions at least. So, plausibly, for any x, if x has the power to create ex nihilo, x is omnipotent (Cf. David Hume, An Enquiry Concerning Human Understanding §7.18, 20).
But now we can bring in the familiar arguments for the conclusion that there cannot be more than one omnipotent being. Quick and dirtily: suppose there are two omnipotent beings, O1 and O2, and that for any x such that x is omnipotent, x can bring about p or bring about ~p. Possibly, O1 brings about p at t and O2 brings about ~p at t. But that’s not possible. For either p or ~p to obtain at t, O1 or O2 must fail to be omnipotent. Thus there can be only one omnipotent being.
So if there can be only one omnipotent being, and creatio ex nihilo implies the creator be omnipotent, there can be only one being able to create ex nihilo. So if a creator created the universe ex nihilo, there is only one creator and the ‘multiple creators’ objection fails. See here for an argument that the objection also fails against Thomistic cosmological arguments.