Why can't I uncheck "Create new revision" on the content type edit page? On Drupal 8, I created a new content type, MyContentType, and accepted all the defaults.

I noticed that Create new revision under Publishing options was checked but slightly grayed out and I could not adjust the value, even though I was logged in as user 1:



I don't know why I can't uncheck it, but this is fine because I always want to save a new revision every time the node is saved.

However, to test this, I then created a new node of MyContentType and saved it.  Then I edited the saved node-- and the Create new revision checkbox is unchecked!

So Create new revision is permanently enabled on the content type edit page, but on the actual edit pages for that content type, the revision box is not checked by default.

What is causing this bizarre behavior?

In Drupal 8.2, create new revision became checked by default, but it says nothing about making it "mandatory by default".
The problem was the Content Moderation module (Drupal 8.4).  I guess I have to take the experimental warning seriously.

When Content Moderation module is enabled, you can't change the "create new revision" status for any content type.

However, content types not subject to content moderation will not have the "Create new revision" box checked on the node edit page if the box was not checked before Content Moderation was enabled-- or if the content type was created while Content Moderation was enabled.

This can be confirmed by checking the config for the content type that has been exported by drush, which shows new_revision: false.  This is most likely a bug so I'm off to file an issue.