Cuz the devs explicitly named it after the peanut butter and even gave it a catchphrase to make sure you pronounced it correctly. It was a marketing campaign. “Choosy developers choose gif”.
The same way? There’s thousands of words in the English language with the same pronunciation and different spellings. This isn’t the dunk you think it is.
Besides, gif existed first. If JIF wanted to use the name without confusion maybe they should have come out first (missed it by half a decade) or come up with a catchy phrase.