Only a small percentage of people buy books regularly. So to make a big bestseller you have to write a book that gets bought by that huge majority of people who don't read much. And usually their decisions are dominated by random extraneous factors: i.e. it's a biography of someone they admire, or is related to some doctrine they subscribe to, or contains facts they need or gossip they want to know about.
Think of the books you find in the houses of people who have hardly any books: the Bible, the Guinness Book of World Records, a Chilton car repair manual, a racy biography of Princess Di, a book of popular mysticism, a book about how to make money or lose weight. Those are the really big sellers.
(This question sounds smarmy, but I ask it earnestly.)
Good judges can tell who the good writers are, but there's no currently no independent way of telling who the good judges are.
Empirically the oscillations of opinion seem to settle down after a few hundred years. Even then there are probably errors. E.g. tragedies will tend to be more highly regarded than comedies, because they seem more serious.
I meant to write: "OK. And because of this Rand isn't a good writer?".
It's not a non sequitur, just a typo.
To save myself from repeating the same argument as the few threads above this, I'll just link to it:
> the popularity of her books suggests otherwise [my emphasis]
In other words, you weren't actually making the claim I thought you were - that popularity implies quality. So I'm sorry for missing your point originally.
I do disagree that popularity is evidence of quality; popularity is only evidence of broad appeal, and you'd still need to demonstrate a correlation between broad appeal and quality - I contend that no correlation exists. But that's a reasonable debate, not a logical fallacy.
But I have to ask - why didn't you tell me that I was refuting an argument you hadn't made...?