you can't "change the password" on a wallet, so a "used" wallet is highly unattractive. anything you put in it could be taken by the original keyholder who sold it to you.
Oh but you can. You can swap out the seed and generate any new addresses using that.
Yes, the old addresses will be compromised. That's fine. The point is that nobody can tell that you aren't actually using the same keys to generate new addresses anymore.
