once a president, always the president?

sorry, forgot to give my signature to this idea: jeannette Marina from the Netherlands, Europe.

I don't understand the question. Are you asking why people are called "President" even after they no longer hold the office? Or why other people don't get as much attention?

both, maybe. Why is the titel in the name? there are enough places where you can put once's experiences of life or you can even make a project to put them together with all the appropriate documentation and URL's to other places on the internet about the work they and others in their offcies e/o neighbourhood made to change our world. groetjes, jMu = jeannette.

Jeannette, major honorifics traditionally become a part of someone's name or title. For example, we wouldn't call Queen Elizabeth II of England just "Elizabeth," because that is not how she is known. Likewise, former presidents always retain the courtesy title of "President of the United States." The same is true with military rank like "General" or "Sgt."), professional titles (like "Dr." or "Rev."), nobility titles (like "Sir" or "Duchess"), and so on.

The display name isn't mean to describe someone's entire life; that is what the "About Me" field is for. So it's not being used in display names as a biography, but rather because that is indeed the person's title.

and when is it done, also with military ranks? and to what extend? generals, admirals, kolonels, ... ?

The highest title is the one always used. For example, Barack Obama was both a senator and president. But he will be called President Obama by historians because that is a higher rank.