But, the problem is that you can't know how safe it is and most of the times, it isn't same like a seed phrase. When you pick a password, your money are vulnerable to the entropy that you, as a human, think it's unpredictable enough.

So why not just let your computer pick a random number, instead of you, which is a proven fact you can't, represented in twelve words? I mean, you can't really find much passwords which are both so strong and short as a twelve-words phrase.