Hmmm...
Maybe by people who thought you were talking about sneakers / plimsols.
Joking apart, it might be a sort of "asssimilation" with the brand name.
I've always said /skaipi/, and was quite surprised to hear people say /skaip/. For me it probably comes from living in Spain, where you pronounce all the letters in a word.
Actually, at the beginning of the success of the brand in France, most people pronounced the name /naik/ , just like "Mike" or "Spike".
A final "e" in a word is never sounded /i/, and if it had been sounded, it would have been like the Greek word for victory, nikê /nike/, in which case it would have been very awkward since it sounds exactly the same as "niqué" which is a slang word everybody understands and which means "f***ed", or "busted", depending on the context.
Not a very good name for a trade mark over here, is it?...