You either don't understand or know what a genre is or are assuming a very narrow definition of it.
EDIT: Here's some text which I hope may be of some help.
From Jim Samson's 'Chopin and Genre' (1989) in Music Analysis, Vol. 8 No 3:
'Genres might be compared with stylistic norms or formal schemata.* All three are abstractions - 'ideal types' - but abstractions whose basic principles flow from actual musical works. All three are based on repetition, codifying past repetitions and inviting future repetitions. Because of this all three can help to regulate the area between content and expression within an individual work, while at the same time mediating between the individual work and music as a whole. Given these parallels and given too the obvious importance of the concepts as agents of communication, it seems worth exploring a little more closely the relationship between genre, style and form, and in particular the differences in their mechanisms.
In its widest sense, especially as presented in some popular music theory, genre is a more permeable concept than either style or form, because a social element participates in its definition, and not just in its determination. In this broad understanding of the term the repetition units that define a genre, as opposed to a stylistic norm or a formal schema, extend beyond musical materials into the social domain so that a genre is dependent for its definition on context, function and community validation and not simply on formal and technical regulations. Thus a genre can change when the validating community changes, even where the notes remain the same. The social dimension can extend, moreover, to the function of genre within the validating community. As several authors have noted in literary and musical theory, a genre behaves rather like a contract between author and reader, composer and listener, a contract which may of course be broken. It is above all in the incorporation of this social element as to definition and function that genre theory in literary and musical studies has developed beyond its presentation in early twentieth-century poetics, notably in Russian Formalism.'
[…]
'Chopin's project and achievement was to give generic authority to the free- ranging devices of an emergent repertory, crystallising the meanings of some existing titles, transforming the meanings of others and devising new titles to meet new generic requirements. In each case there is a measure of consistency in the semiotic relation of the title to the formal and stylistic features of the piece.
As we know, the "sign" is bipartite, and both parts are essential. The title is integral to the piece and partly conditions our response to its stylistic and formal content, but it does not create a genre. Equally a taxonomy of formal and stylistic devices will not of itself establish a consistent basis for generic differentiation. It is enough to consider the substantial overlaps between Chopin's genres in this respect. Without the title we might have difficulty classifying even some of the nocturnes. It is the interaction of title and content which is important.'