As discussed in this post, a question must have at least one answer by a user with less than 10 reputation in order to be protected by a 15k+ user.
For example, here’s a question that’s several years old with no answers by low-rep users:
Clearly there’s no protect option.
The protect option shows up normally on another fairly old question with a post or two by a <10 rep user.
However, the protect option is also present on any post whose only answers are by users whose accounts were subsequently deleted, for example here and here, regardless of how much reputation they originally had:
Is this a bug?