are there password managers for Apple TV?

Not directly.

Your AppleTV will be associated with your AppleID (the same AppleID you likely use on your phone, and to log into these forums. As such, it has indirect access to passwords stored in your keychain, but there's no separate app on the AppleTV itself to manage your passwords - you usually do that on an associated Mac or iOS device.

Who says you have to do that?

Do you have an iPhone? You do realize you can use your phone to control your AppleTV, right?

In this case, whenever your AppleTV prompts for a password (or any keyboard input), you can use your iPhone rather than the on-screen keyboard. You can copy passwords from your keychain and have your phone enter it on the AppleTV. No paper required.

You are absolutely correct.

BUT … if you have an iPhone or iPad on the same AppleID, using the keychain w/ the “Remote” contained within Control Panel is relatively pain-free.

Just an option …

Your point is well taken.

Using an AppleTV can indeed be greatly aided by using iOS devices.

While we can’t comment as to how or why the AppleTV design evolved to it’s current state …

… you CAN provide your feedback to Apple and possibly influence future development here:

Feedback - Apple TV - Apple