Based on what I had read and been exposed to at the time.  Not having an income of my own and very limited transportation, I didn't get to explore as much as I would have liked.  I'm not certain I'd been to any science fiction cons at that time!

I know they were there, it was just my own discovery of them at that time was sorely lacking.  My (very young and misguided) perception was that they were mainly 'fantasy' authors, and at that time bookstores frequently has different sections for science fiction and fantasy, something almost unheard of today.