Enrique, my apologies. I thought you were joking so I wasn't taking your question as seriously as you intended.
If you think back to 7th grade English, the capitalization you are talking about fell under the category of "capitalization to show respect". That is, we capitalize words like God, King, President, Duke, Pope, Bishop, etc., not because they fall under other rules but as a sign of respect.
Technically, the strict rule would be not to capitalize when used as a noun, but capitalize when used as part of a name or as a pronoun.
But, the rules have changed in our lifetimes, and the rules continue to change. Capitalization generally falls now under "style" rather than "grammar". Fewer people nowadays accept that we all owe the old peasant deference to the nobility and clergy, for example. Then too, there is a strong trend away from capitalization in general, and especially where (like this) it is a special case.
This article makes the point:
http://grammarist.com/capitalization/
It says, for example, "there is much disagreement over when to capitalize. Every major publication and publisher has its own standards, and many writers have their own preferences (which are generally overridden by in-house rules during publication)."
And, "the best rule of thumb for capitalization is to err on the side of minimalism."
Then -- because I know you won't believe it without a concrete example -- here is a style guide that specifically recommends the usage you're complaining about:
https://www.englishforums.com/English/NounCapitalizationQueryBishop...
It gives these examples:
* "Bishop Smith will be speaking today." -- capitalized title before a person's name
* "Johann Smith, bishop of XXXX (place) will be speaking today." non-capitalized title after a person's name.
* "Good morning to you, Bishop." -- direct address taking the place of a name is capitalized.
* "We will need a bishop to speak at the ceremony." -- non-capitalized when not referring to a specific person.
This is the style guide that can be inferred from most of the academic history I read, although I don't know the specific source.
As a former editor, this is also the style guide I use myself.
Personally, the style that makes me nuts is the modern news headline style that capitalizes every word. So -- Bishop Of Metz (*shudder*). We all have our buttons ;)