IDK, really think you’re overthinking this one? Why do people assume he wears glasses? Maybe because Edward Ngyma has very commonly been portrayed wearing glasses? BTAS is one of the only pieces of media in which Riddler’s alter ego DOESN’T wear glasses. There’s no alter ego in 66. Carrey wore glasses in Forever. Gotham has Ngyma wearing glasses. The Arkhamverse Ngyma wears glasses. Various animated versions wear glasses. Add in the serial killer angle and it only makes it stronger.
It’s like Penguin’s monocole or top hat or Mr Freeze having goggles. Sometimes they have it, sometimes they don’t, but it’s an established part of the characters iconography.