Where is my apple id password stored?

It may be saved in the Passwords app under "Apple" if you ever logged in to the https://account.apple.com website.

But it does not happen automatically otherwise. You should remember or add it yourself if you need to have it stored.

Usually on Apple devices where the Passwords app exists, your Apple ID password is superseded by Touch ID or Face ID even when logging in to the https://account.apple.com website so the password is not directly used though.

We cannot know why Apple chose to do it this way though so no way to answer "why".

You can offer Apple feedback at https://apple.com/feedback if you would like to be added automatically.

crmark wrote:

Tried to reply and apple keeps kicking me out? Why??!!

This reply went through. The forum may have been experiencing some issue when you tried to reply originally though.