Most of them are build without having decrypted passwords or keys for them on server, so attacker would need to get to the point where they can craft malicious update to the client (or exploit the client)
2. Inject code in build to export user's passwords to remote server after update is installed
An offline password manager is updated a few times a year, and will go through OS repository distribution, with verification of the signature for changes. Or you can download the software from the source website and check the signature.
Now that's not to say that something can't be sneaked into other work! But the bar is a bit higher than "take over a dependency"