At beginning, Internet used network classes, because of hardware limitations (later switched to address blocks). And even in 1990s still existed very old hardware, only could use class addresses.
What classes mean, existed early very large organizations, got more addresses than they could use. And even happen few cases, when such organizations lost rights for these addresses.
And these unlucky organizations was some big whales, like IBM or ATT/Bell or Sun.
And once invented solution - state some big enough network as not allocated to use under NAT (or when network is not connected to Internet). So, departments of big organizations could use TCP/IP stack in their networks, even with old hardware, but don't need to contact Internet officials to got real internet addresses.
192.168 was just first C-class network prefix, was not assigned at the moment (or just released).
Later, to list of unassigned added 172.16/12 network.