I am not sure why you are taking this so personally or why you insist. It is an English notation and looks foreign in most of Europe, for example. I can say for sure that it is not “in all of them”, as I used to live in such a place. The only contact with AM or PM in daily life is in poorly localised software, and is completely foreign.

They use 24 hour time in most contexts, but often use 12 hour time informally and the actual time is understood in context. You might not believe it, but this happens.

It is, in fact, not unreasonable to ask for an option to format time in 12 hours without letters after. (I am not saying the author should do it; they are the one to choose what to do in their free time).

Settings like date and time formatting and physical units should ideally be changed by the user. You cannot expect a single setting to work all the time.