I suppose for a few reasons:
First, it strikes me as absurd to call the Enterprise immaterial. If someone understood the Enterprise to be immaterial, they’d have to clarify that in conversation because we’d naturally assume they meant something material.
Second, as Van Cleve states, “[t]he Aristotelian position [hylemorphism] leads to a problem that Ernest Sosa has dubbed “the explosion of reality”. To be drawn into the problem, ask yourself the following question: which aggregates of matter and which forms are such that when those aggregates come to exemplify those forms, a new entity is thereby created? It seems to me that an impartial Aristotelian ought to answer as follows: wherever
any matter instantiates
any form, a new entity is thereby exists. Consider, for example, the entity Sosa calls a
snowdiscall, which has as its matter a chunk of snow and as its form any shape between being round and being disc-shaped. If you take a snowball and flatten it, you destroy the snowball (having deprived it of its essential form), but you leave a snowdiscall in its place. Moreover, the the snowdiscall you leave was there all along, sharing matter with the original snowball…From here it is but a short step to the recognition that an impartial Aristotelian (or “absolutist” as Sosa calls him) should admit that there are millions of of entities inhering in any parcel of matter. Consider the following series of shapes: being round, being round or flattened up to degree 1, being round or flattened up to degree 2, and so on, until we reach the property of being round or flattened up to some degree including being squashed into a disc. We may distinguish infinitely many such shapes. From an impartial or absolutist point of view, each of these shapes has as much claim as roundness to be regarded as the essential form of an entity of some type. An ordinary snowball, it would therefore seem, coincides with infinitely many other entities - snowdiscalls of all possible degrees.” Sider, Theodore, John Hawthorne, and Dean W. Zimmerman.
Contemporary Debates in Metaphysics. Malden, MA: Blackwell Pub., 2008. p. - p. 324
Seems like many would reject such a position because of its bloated ontology (the reason most reject Lewisian Realism), but as Van Cleve later notes, this position seems to violate the impenetrability of matter principle, which I take to be more plausible than hylemorphism: Two or more things cannot be in the same place at the same time.
Instead of snowballs and snowdiscalls we could use the Enterprise and get the same result.
Edit
I’ve seen this argument before, Zimmerman advanced it as a modified version of Chisolm’s
Entia Successiva argument in
Contemporary Debates in Philosophy of Religion.
But, really, this species of argument is just a rehash of the ol’
Theseus’ Ship Paradox.