With monopoly cases, it's all about market share. In the late 90s, Windows had 95%+ of the market[0]. I believe (but may be mistaken) that the legal threshold often used is 75%. Apple isn't there, but Windows certainly was.
since when does market share determine what competitors there are? competitors are businesses competing against each other for the same market share. so your chart actually proves my statement since both linux and apple existed at this time.
