The current web based password manager services save your password on cloud. Your's data is owned by the cloud service provider.

All sensitive data is at one place. In case of a breach, blocking all payment options and changing passwords for all accounts might take enough time for the attacker to do damage.

If the server breaks down, your only hope is that your provider has made a backup copy.

Not all devices are secure enough. Hackers exploit the same vulnerability to get all of your logins in one attack.