From its very early days, the Unix OS was deliberately designed and coded with the tacit assumption that multiple programmers would work on the system. Thus, the culture of writing clean, elegant, and understandable code, to be read and worked upon by other competent programmers, was ingrained.
Later, with the advent of the Unix wars, proprietary and legal concerns overrode this sharing model. Interestingly, history shows that the Unix's were fading in relevance and industry use, until the timely advent of none other than the Linux OS – an open source ecosystem at its very best! Today, the Linux OS is widely acknowledged as the most successful GNU project. Ironic indeed!