Like I said to the other commenter, the source code for the software being discussed already is available - by definition - and much more easily than if you had to go searching through /usr/lib. It's an absolutely moot point[0] whether Apple bundles the source code for Bash into their operating systems, for 99.99999% of intents and purposes and users.

We're not discussing whether the source code for XNU/Darwin/Mach/MacOS itself ought to be open, which is another question entirely. (Obviously everyone would sooner it be open than not open, in a first-order analysis, but, as with medical patents and the like, a proper analysis would have to ask whether it would even have existed if its source code were to be open.)

[0] Or rather a non-moot point, for the pedants.