The reason why it's not unreasonable for German is because those digraphs were the origin of umlaut. You have a vowel that is roughly in between "o" and "e" as

The reason why it's not unreasonable for German is because those digraphs were the origin of umlaut. You have a vowel that is roughly in between "o" and "e" as used by Latin, so you start by writing it thus: oe That feels too long, so you make it a digraph: œ Some people still think that's too long, so you start putting "e" on top instead: oͤ That tiny "e" on top is kinda tricky to write in full, though, and slows things down, so handwriting eventually trims it down to just two vertical strokes: ő Lastly the strokes themselves become shorter and shorter until they become points: ö But since it's been "e" all along, the old convention still remains, and is arguably just as German as the umlaut diacritic. It's not something imposed on the language from the outside, as is usually the case with latinization of non-Latin-based scripts. Coincidentally, this is also the origin of Swedish å (literally "o" over "a") and Spanish ñ (literally double "n", with one written on top of another)