I think this is exactly why people have a hard time with this advice. We're used to thinking we owe the author something because we've chosen to read their book

I think this is exactly why people have a hard time with this advice. We're used to thinking we owe the author something because we've chosen to read their book. What this presupposes is that we owe them nothing, in fact it's up to them to justify spending our limited time and attention on their book, rather than in the million other options for books available to us. You will occasionally miss out on a good one by following this advice, but in the end you'll read so many more good books, because you'll spend less time halfheartedly slogging through books you hate and dread.