Yeah I know what you mean, it is kind of ridiculous but I have seen this trope in multiple places even in things that are not yaoi. Σ(っ°Д °;)っ
As an example when I was a kid my family had this really old superman show and LITERALLY the only difference between him and his superman identity was that he wore glasses. So many times when characters have no idea who this other person is whether it is because they are a love interest, or they lead a double life, having seen this MULTIPLE times I am not so much annoyed as I find myself laughing at the stupidity of the people in the story. (︶︿︶)＝凸
Come to think of it Sailor Moon also follows this cliché of I-wonder-who-that-person-is-even-though-it-is-super-duper-clear-we-are-all-idiots-while-the-show-is-on-air sort of thinking. So yeah it is ridiculous but strangely I have seen it used in many places such as books and tv, that I have kind of gotten used to it by now when a person can't recognize someone who has a special significance to the main character when they are literally standing right next to them. Σ(っ°Д °;)っ(⊙…⊙ )
And many times the ONLY difference is they are wearing glasses, or they are dressed in a different fashion which seems to have a magic effect on the main character that makes them unrecognizable. (╯°Д °)╯╧╧
So it is ridiculous and far fetched but it has come to the point where I treat as another cliché that pops up in story writing and leave it at that.(⌒▽⌒)
I am not here to say using this cliché makes it bad, nor unenjoyable I actually enjoy reading stories that use this cliché in stories where a character can't recognize someone they are close with I just find the unrealistic aspect to it humorous to watch regardless if it gets found out or not by the characters in the story.ლ(´ڡ`ლ)
It happens irl too. There was a Charlie Chaplin look alike contest once and Charlie Chaplin himself entered the contest.... and he lost!
There is a similar story about Robert Downey Jr.
Not the superheroes
Ok, I get the first guy was an idiot, but seriously "I am really in love with my manager, but if he puts on different clothes, I can see him once a week and not recognize him"