You didn’t, I note, say the quiet part out loud, which is that a self-published book is just less likely to be any good than one published by a publishing house. For every Walt Whitman there’s literally a million terrible poets. Hundreds of books reach the slush pile and a scant few rise to the top. That’s not because the deserving always get recognition, but you also can’t say that quality has nothing to do with it. And a self-published book often hasn’t even had an editor. And then amateur writers with little experience of getting edited, critiqued and published can be very touchy and bad at taking feedback. But you didn’t need to say any of that because the reasons you gave are plenty in themselves.