The line comes from the long tradition of roses are red verses, a simple rhyming form that has been rewritten as love poems and jokes for generations. In Portuguese, as rosas são vermelhas works the same way, instantly setting up a rhyme listeners expect to complete. Short versions like this one spread as WhatsApp audios, forwarded between chats and reused on soundboards because the setup alone is recognisable, even without hearing the ending, and it fits romantic teasing as well as parody.