Books selling the wisdom of our grandmas: my guess is that only the old ones will read them. The young ones already know everything!

.... that is what idioms and sayings do, they brighten up the language with wisdom and fun. Language, the words you speak aren't so dull. It's a shame how few [idioms] the present generation know....

You are right! Even my own children who've heard me use idioms can't say what they really mean.
"Pot calling kettle black" - clueless.
"Waste not, want not" - they don't know that to be "wanting" means to be lacking money, etc.
Even "agree to disagree" is lost upon them.
Schools are too busy teaching that there are now 90+ genders....