Singlesig advocates always tell you to create a Passphrase, why?

This is because no matter how secure your Seed is there is a chance it can be compromised to a degree. This already gives you multiple secrets to hide separately & hopefully you have your seed words backed up in more than one location/copy.

If you have generational wealth to secure you're better off creating a 3of5.

3 unlocks the wallet, with 2 redundancies.

You store the wallet coordinator file with each seed, as well as storing a few copies on separate USB sticks at home - & in an encrypted email server like protonmail.

So you basically have 5 secrets to hide with a coordinator file to store which you will need.

Obviously this comes with complexity, but storing a shit load of money requires assurances.