Berkeley was paid to port TCP/IP to unix and as far as I know, part of the deal was that the code should be available to quickly port TCP/IP to more systems including non-BSD.
Thus considerable portion of Operating systems at one point or another used BSD4.3-derived network stack to detriment of network API evolution (sometimes updated with later code), some over time developing their own implementation.
Thus considerable portion of Operating systems at one point or another used BSD4.3-derived network stack to detriment of network API evolution (sometimes updated with later code), some over time developing their own implementation.