Because 'cloud' is a familar cognitive trope. But do clouds possess form at all?
In the older sense of eidos, yes. Clouds are intelligible and sensible. If they lacked form they couldn't be experienced as clouds.
(That question is anticipated in the Parmenides, when Socrates asks if there are forms for hair, dirt and mud.)
Yes, it's a problem crying out for clarification. Aristotle has the distinction between "things that exist by, [i.e. according to their], nature"—beings which possess a telos—and things that exist "from causes." But I don't think Aristotle's distinction gets at the full scope of the problem here. Plato's forms, at least if taken in terms of some "two worlds Platonism," where forms exist subsitently and not in relation with one another, is also problematic because things are not wholly intelligible in isolation, e.g. "redness" as set off from "color" and all the other colors. For example, you can't really explain what a "tree" is without reference to the air, the sun, the soil, water, etc. Forms are not intelligible in isolation.
Aristotle doesn't do much with this second problem but it is addressed in later thinkers, St. Maximus the Confessor being a prime example of an advanced synthesis that is able to distinguish between the unity that contains all ideas/forms (the Logos) and their dynamic instantiation in the created world. Hence, even "number," "hardness," etc. are dynamic in precisely that they only exist instantiated in created things, but exist according to their "logoi," which is ideas "at work" in the world. The idea of species as all being differentiated expressions of a unifying genus progressing towards the unity/whole and goal of the genus would then be a further working out of this idea.
For the pre-moderns, obviously forms could have 'eternal reality in the mind of God' but that is generally not an option for modern philosophy, but we could plausibly say that the idea of forms arose from an intuitive grasp of this co-dependency.
It's not an option for good reasons or out of bias? "Thou shalt not explain ideas in terms of the transcedent or absolute," yet one can apparently offer up explanations of anything, and indeed everything, that bottom out in brute facts, "it just is," and "for no reason at all." And things even seem to be allowed to bottom out as brute facts isolated in the sui generis powers of finite minds, such that the mind "just is," the source of all sorts of things in the world, including Goodness, Truth, and Beauty.
IDK, this strikes me not so much as contemporary philosophy being opposed to positing God as part of an explanation as contemporary philosophy wanting to make man
take the place of God. (But of course, a voluntarist God, whose freedom is defined in terms of power and potency.)
In any case, the fact that forms are artefacts of the cognitive system, does not undermine their objective (or would that be transjective) reality. It doesn't say that they're solely the product of the mind, but that they arise in the relationship between observer and observed. Biological phenomenology such as enactivism sees such cognitive artifacts as co-arising as a consequence of the interaction between organism and environment.
I don't see how enactivism would require that forms are "artefacts of the cognitive system." This sounds like something leaning more towards representationalism, forms as "constructed intelligible likenesses," that must be created "in the mind" to be experienced. But of course, if things are already likenesses of themselves and if we're talking about an enactivist perspective, there is no need for having there be secondary likenesses "constructed for the mind." E.g., the idea of the cognitive/sensory system as a lens we "look through," as opposed to producing images we "look at."
Perception arises in the relationship between observer and observed. It seems another step to say that form would arise from this interaction, since it would imply that the world is unintelligible and without causes before the human mind steps to the plate and declares "let there be light! Or form, or anything at all." And of course, we can never get behind this act of the mind to explain it in terms of causes, for all causes and intelligibility start with the mind.
Like I said, this strikes me as not that different from approaches that invoke the divine, except man is fills the role of God.