I think it has more to do with the complete lack of testing infrastructure and tooling that Apple has produced over the years, despite the explosion of APIs and developers on their platforms.
Even on iOS, which rumors have being more of a focus compared to macOS, still has a long way to go to catch up to other platforms. If they required these tools internally, no way would they be this far behind.
Can you elaborate on what's missing? I do a lot of graphics work, and their macOS debugging tools for OpenGL were terrible, but the ones for Metal (which came out first on iOS) are pretty cool! I also use Instruments a lot and some of the other more esoteric tools supplied with Xcode. Not to mention the static analyzer, Address Sanitizer, and lately the Undefined Behavior Sanitizer. But I'd love to have even more tools! What else is out there that they don't supply?
I am talking specifically about unit testing, ui testing, integration testing and then supporting those tools in some type of ci system.
And to be clear, they provide these things in the form of XCTest, XCUITest, and Xcode bots, but they aren't good enough. Tons of resources have been spent by the community and major corporations trying to fill in the gaps and offer useful alternatives, but the closed nature of Xcode and its build environment make this difficult.
Even on iOS, which rumors have being more of a focus compared to macOS, still has a long way to go to catch up to other platforms. If they required these tools internally, no way would they be this far behind.