This is the sort of arrant pedantry up with which I will not put

I spent a solid ten minutes researching this and couldn't find any suggestion that there's any problem with the title.

Could you explain how it's ungrammatical?

There’s an outdated rule in English that states you shouldn’t end a sentence with a preposition. It dates back to a time when writers applied Latin’s grammatical rules to English. It’s mostly ignored now.

But... it's a title, not a sentence. Many book titles are even a single word, which is even less a sentence. Why would a grammatical convention for sentences apply to book titles?

Heck if I know. All I know is I am a lot more worked up about the misuse of “less” when the correct word is “fewer”.

Whom would care fewer?

Which itself was simply the preference of a spinster who wrote a grammar book.

English has no rules like that, only preferences.

They did, they just understood they were editing English not Latin.