I did most of my work on Unix before I started at Apple in '95. All of the new OS development was being done in C by then. I suspect that before most of the OS development had been done in 68K assembler, not Pascal. When the switch to PPC started, Apple needed a cross-platform systems programming language and Pascal was not it.
This article from '93 references how the industry mindset had switched to C/C++ and that pushed Apple.
https://www.schneier.com/essay...
One thing to remember is that at that time, both Macs and PCs were not very powerful machines and large applications were being developed for Unix workstations.