It went with Objective-C because of Nextstep. Apple bought NeXT because NeXT had a real operating system and Apple didn't. Apple had burned a few years and a hundred million dollars or so trying to build a proper operating system, and they weren't very happy with what they had to show for it. So they bought NeXT.
The application layer of Nextstep was written in Objective-C. So Objective-C became Apple's new application-programming language.
By the time of the NeXT acquisition, Pascal was already out of fashion. Apple's officially-blessed application framework, MacApp, was originally written in Object Pascal, but Pascal wasn't particularly popular with programmers inside or outside of Apple. People liked C better, and most of them used it whenever they could.
When it came time to plan for development of MacApp 3.0, the development team was hearing a lot of complaints about Pascal and hopeful wishes about C. I remember a meeting where Steve Friedrich, the lead developer on MacApp, wrote down all the options he could think of on a whiteboard and crossed them off one-by-one. All the objections boiled down to what programmers inside and outside Apple would put up with. The last thing left on the list was C++, so MacApp 3.0 was written in C++.
Only a handful of programming-language nerds complained about the change. Ironically, one of the complainers was Steve himself. He was a Smalltalk guy, but he was there to give Mac developers what they wanted, not to push his linguistic preferences.
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