Note: Every BIP39 seed phrase has a passphrase.
That's why no one can tell if your wallet uses word 13 or 25. A different passphrase creates a different wallet, with no trace of the original.
The most common inheritance plan in Bitcoin is called "we'll do it later."
We'll explain it to our partner later. We'll test it later.
That "later" usually ends badly.
If you're not around tomorrow, who will move your BTC?
Answering your last question from the other side: I’m the non-technical one in our house, so I’m the one who would have to move it.
Your first point is the one families miss. Without the passphrase, the words alone open a different, empty wallet. So the person left behind has to know the passphrase exists, where it is, and where it goes.
We stopped saying “later” by testing it while we’re both here. I followed my husband’s written steps alone, with him watching and not helping, through to sending a small amount from the passphrase wallet myself. It took a lot of rewriting before I could. Now our steps say exactly where the passphrase is typed, and where it must never be typed.