If you’re on Windows, I imagine there’s a copy of your file somewhere down in the roaming directory. How else could your application undo your last 6 changes?
A password manager performs additional tasks for you, like deleting passwords from the system clipboard after 15 seconds or shutting down your database after you forget and walk away. If you’re tired of always having to think of new passwords, it can generate new ones with a specified level of entropy. Some can send the username and password directly to your current webpage. The online managers can fill out forms for you (though, in my paranoia, I don’t use online managers for bank accounts). The online managers will also offer to capture the information you’ve created for a new account so the whole process is seamless. Some managers (I understand, don’t use it yet) can use authentication devices (yubi-key) to login, providing additional security. Others will let you use a “secret” file as an additional security component, so even if someone has your file they can’t brute force it.
So, off hand, there doesn’t seem to be a lot of compelling reasons to use a spreadsheet, unless there’s some special case business reason.