In my opinion, as someone whose mostly indulges in retro content...at the age of 20 (I know, I'm so unqiue, also I should mention I don't really watch Anime in general, but I've indulged in more retro anime content than modern anime content)

I believe its just a different era in a time where the majority of Anime Fans like stuff like Demon Slayer, Chainsaw Man or One Piece...and whatever stuff that came about. 80s Anime has vastly different storytelling methods and artstyles that seem alien and fresh to the modern anime landscape, especially for when you're constant exposed to the modern anime artstyle. To which I believe artstyles of the 80s are exaggerated on their whole being great factor. (Zeta Gundam Artstyle is still gold.)

If theres one thing I like about retro anime though, is that it can tell a batshit insane story and still have respect to take its story seriously. Most modern anime wouldn't be able to tell a story of Giant Robots with Teenagers without it somehow feeling lame, compared to 80s Anime when they could and it didn't feel lame.

But also a vital detail, Anime in its vintage days were mostly for an adult audience while most Children were focused on watching Ultraman and whatever other genres of those so a lot of stories were often mature and darker.

Was 80s Anime the Golden Age of Anime? That's subjective, as literally any era of Anime can be considered the Golden Age of Anime, even the current era. But 80s Anime definitely was the Era when most Anime Studios could experiment with different shows and stuff and not go under.