It was the early '80s. The word "cosplay" hadn't even been coined in Japan yet, and it would be a couple of decades before it became a recognized subculture in the US. At the time, dressing up as a superhero in public was seen as "weird."
Really, the thing I noted about TGAH the last time I got a chance to see it was that it was very much a product of the era before superhero fiction went mainstream, before Comic-Con became the touchstone of pop culture and normalized things like public cosplaying. There have been other deconstructions of superhero tropes since then, but what makes TGAH different from more recent ones is that it isn't an affectionate deconstruction; rather, it treats the whole idea of costumed superheroes as a target of scorn, something the characters are embarrassed to be involved with and that the people around them react to with shock and disapproval. It's a mindset that's hard to understand today, when pop culture is so in love with superheroes.
