The story here is that the creator didn't make any kind of real effort to make his pronunciation known, despite the internal slogan "choosy developers chose gif" with a soft g, ala the old Jif peanut butter slogan.
The tech world, not being awash in youtube in the late 80s, saw this primarily in print and most people (though not all) went with the more intuitive* pronunciation with a hard g.
And
usage is king. The hard g isn't going away, and the soft g is just fine.
* Most of these (but not all) start with a hard g, and if people had the word "graphics" in mind, that might have also swayed them subconsciously.
words that start with gi, words starting with gi, words that begin with gi, words beginning with gi
www.thefreedictionary.com