Unfortunely did not come with an OS, wasn't freely available, and quite costly.

Remeber that until AT&T was allowed to take commercial advantage of UNIX, its source code was available for a symbolic price, and it came with a C compiler toolchain, at least until Sun started the trend among UNIX vendors of spliting UNIX development tools into an additional purchase.

The UNIX vendors that had Ada compilers, that was an additional purchase on top of UNIX SDK (which already had C and C++), so unless there was a hard requirement to use Ada, no one bothered to pay extra.