The Johns Hopkins Guide to Literary Theory and Criticism doesn't have entries for poetry, poetics, rhythm, meter, prosody, music. Other anthologies of literary theory don't really include these topics either. When I taught literary theory myself, I didn't include them either, despite my deep interest in these subjects.

So clearly the idea of "theory" does not tend to encompass prosody. Just sayiin'.

What else does theory exclude, and we don't even know it?