Thanks a lot for your insightful comments, Clive!
Now, I was wondering if the reason weren't one of closeness or affection, i.e., as "Nike" is an American (national) brand, and certainly, one of the brand leaders, I thought that Americans may want to show or express a certain liking or closeness through the addition of the sound /i/, as they do with other words to evince this type of feelings:
E.g. cutie/cutey, kitty, sweetie, even Tweety (the fictional Warner Bros. character). All these words show a feeling of closeness or affection towards the object.
I know that the pronunciation of the sound /i/ at the end of all these words comes from their very spelling, which is different from that of "Nike", but couldn't this be done by extension?
Maybe, some Canadians say /naiki/ as well for their country's nearness to the US, where they hear it pronounced that way.
What do you think about this, Clive?