It took me very little detective work to determine that you ...(drum roll) are me.
No wonder I almost posted the above.
> I judge books by their covers.
On second thought, although I like great covers, you're not me. Carry on; you do you.
(Yes, I know - the phrase means "Look past surface details and see inner beauty" and so on. It's just that for books the heuristic works pretty well).
The way a book is advertised absolutely tells you about the book, in most cases. There is a series of thought and decisions which go into making a cover, including finding a compatible artist and giving them a solid brief.
As with fast food, there are exceptions... But they are exceptions. It may be more of an heuristic than a rule, but it's undoubtedly often useful. The cover is part of the book, and an important part; both up to and beyond the advertisement.
https://duckduckgo.com/?t=ffab&q=the+expanse+book+covers&atb...
You see they're in space, you get the impression that there's ships, that it's gritty, that it's sci fi, etc.
None of those images look a million miles from the tone of the series, much less outright misleading.
If there are exceptions to that, then they're exceptions to a clear general rule; much like with fast food menu pics.
And while it's true this can neither vouch for nor indict the writing itself, the rest of us are allowed to enjoy the art just the same.
Besides, the new digital era debunks your claim... cover images are still included in epubs even if those do not sit on the wire rack next to the cashier at the store.
And there is taste to consider too. Good books get good cover art.
Or do they?
Marketing material is often the best reference you have to discover what something is about. Also, the pictures of food on a menu usually inform you better what you'll get than a realistic picture.
Marketing has many functions, a large share of them are hindered by misleading you. A few are not. The result is usually very transparent (but effective).
"Thoughts about a thing" is a kind of cover too. Portable, personalized, communicable. Wildly popular.
Does it get at the inner reality? Maybe, maybe not. Is it useful? Yes.
Science could be called a cover optimizer.
¯\_(ツ)_/¯