Including full titles in the salutation of a letter—especially for many nobles at once!—would be inappropriately grandiose in all but the very most formal of circumstances. The vast majority of the time, you will be writing to someone in only one of their capacities—usually the "highest", though not always—and it would be much more appropriate to only address them as "King Kepler" or "Warder of the Church Kepler". Furthermore, most such titles have a mode of address that would be considered to be more correct when addressing them directly ("Your Majesty," "Your Holiness", "Warder", etc), which our current title system does not capture in any way.
It would certainly be nice to have those modes of address alongside the titles in the system; however, that's significantly more work.
All in all, I could see possibly adding an option on a per-message basis to automatically add in a single title in the salutation.
In general, though, if you're playing a game like BattleMaster on your phone, while I am more than willing to try to improve the experience in many ways, this game is centered very heavily around written messages, and until your phone has a telepathic interface, there's no way for the game to know what the "right" mode of address is for any given letter.
