Because either way if it's a weak passphrase you're going to loose your BTC.
Not necessarily. For hardware wallets, the attacker still needs to extract the seed. On Trezor devices we now know that can be done for less than $100 with fairly basic components. As far as we know, other devices still require high tech equipment and the expertise to use it. Very few people have the access and skills required, and hiring such a lab would cost several thousand dollars at a minimum. It's simply not a concern for your average crypto user, but is a concern for people holding large sums of money who are being specifically targeted by criminals.
Sorry to be a downer, but it just gets to me that this is out there and yet they are still selling them and people think they are safe just using an 8 digit pin.
Nothing is 100% safe, and if you have access to additional options (such as passphrases) which increase your security, then I would always opt to use them.
Well, it would be quite unique to have a multi-sig with one trezor, one ledger and letsay a bitcoin core wallet, then a two word phrase is enough as long as the attacker does not know which one is which.
There are even cooler methods but should not be disclosed as of yet...