It seems like it's always the same handful of texts. Ancient readers liked what they liked and weren't out for variety it seems.
At the same time, Juvenal has a whole satire about how everyone is trying their hand at writing books and mentions in another how booksellers are always getting new volumes.
I spend way too much time pining for the chance to read the other parts of the Trojan Cycle, even though the ancient said they were much lower quality. Like your favorite show getting canceled.
Also, Juvenal was a poet. He most likely knew other poets, or aspiring poets, or at least people who liked writing. Your average, generally functionally illiterate, individual at the time is not trying their hand at writing books.