Quite a lot of NeXT was ObjC (and ObjC++ -- eek!). Apple bought NeXT; the NeXT team begat Mac OS X; Mac OS X thus ended up being ObjC-heavy.
When Apple build the iPhone, they used their Mac OS X know-how to build a new-but-familiar operating system, and they of course used Objective C.
The iPhone was a massive success, and the native development language for it was Objective C, so when they opened up the platform to third-party developers, Objective C was all of a sudden an overnight success!
Kind of, they also introduced Java as OS X system language alternative, with a Objective-C runtime interop, as they were uncertaint that the Mac OS developer community, raised in Object Pascal and C++, were that keen in adopting Objective-C.
Java as official OS X language only got deprecated after it was clear the Mac OS developer community was keen in adopting Objective-C.
Also the Objective-C driver framework from NeXTSTEP was rewritten in an C++ subset, based on COM's design.
OS X being a success let the iPhone be built six years later. That may be only a little over a quarter of the history at Apple now but thats the end of the beginning.
When Apple build the iPhone, they used their Mac OS X know-how to build a new-but-familiar operating system, and they of course used Objective C.
The iPhone was a massive success, and the native development language for it was Objective C, so when they opened up the platform to third-party developers, Objective C was all of a sudden an overnight success!