> The word Mississippi itself comes from Messipi, the French rendering of the Anishinaabe (Ojibwe or Algonquian) name for the river, Misi-ziibi (Great River). [1]

I guess technically it’s the Anglicized French transliteration of the Algonquian name that stuck. Why that happened has more to do with the French-Indian war.

[1] https://en.wikipedia.org/wiki/Mississippi_River#History