That ship sailed nearly half a century ago. All of this source code was previously licensed to research universities starting in 1975. The earlier releases weren't under FLOSS license like we know them today, but with the intent that researchers would be reading, learning from, and modifying the code. And they did! creating later BSD Unix releases with more open licenses whose code was shared more widely under more permissive licenses.

Finally, the people who created this repo are some of the primary authors of the code. They wanted this to be in the open.