Because OSI is not a protocol suite. TCP/IP is actually a protocol suite that is implemented on pretty much all networked hardware anywhere.
OSI model explains generically how any network works. It's just a framework.
TCP/IP model explains specifically how the TCP/IP protocol suite operates. Appletalk, IPX, decnet work differently and their models might not look like the TCP/IP model. But they would still be applicable to the OSI model.