The character with amnesia trope is perhaps so popular because it gives the writer carte blanche to be extra liberal with exposition and pose obvious questions on behalf of the audience - which can make it a bit of a crutch in my opinion.

It's a setup that offers an easy excuse to literally explain everything explicitly rather than weaving information into situation, context, etc.

Exposition isn't necessarily a bad tool in the writer's toolbox, but it is one that I think sees disproportionately more overuse. Specifically, to spoonfeed the narrative to the audience.

Anime and manga are notorious for grossly overusing exposition - to the extent that you literally have characters standing still while they explain their origin, their powers, their motivation, what's going on, etc. It's just bad writing.

Captain Ahab would be proud though.