iCloud and iCloud keychain are not really the same thing. iCloud keychain is designed not to disclose user passwords in the event of an iCloud account compromise, for example, among other things. The iOS Security Guide[1] has more details on this topic, starting on page 45.
That's not to say other solutions can never be as secure, but it's a fairly good design nevertheless.
That's not to say other solutions can never be as secure, but it's a fairly good design nevertheless.
[1]: https://www.apple.com/business/docs/iOS_Security_Guide.pdf