>It's all about appealing to the most people as quickly and cheaply as possible

But if you learn actually nothing, how can you appeal to anyone?

>If I have never heard or read those books, those lines mean nothing to me. It gives me no information about what the book is aboutx characters etc.

That's not true.

The first one tells you that it's most likely some form of sci-fi (post apocalypse - world being destroyed) and that it's slightly irreverent or at least weird (what do towels have to do with this?)

The second one literally tells you that it's set in Regency England and is a novel centered around romance and social class.

The third one strongly implies dystopia of a specifically authoritarian nature.

The point is that this is all vastly more information than saying "this book is good" gives you.