Earlier quoted context omitted.
I'd say lack of QA. Apple Music (especially on macOS) is EXTREMELY buggy, unresponsive, slow, and feels like a mess to use. Same for iMessage. Other apps are also written using the same stack with almost no bugs. I wouldn't blame the language here, but the teams working on them (or more likely their managers trying to hit unrealistic deadlines).
No, I would not blame the teams or their managers. You can't just blame a manager you've never met just because he's a manager, we're talking about the manager of Apple Music, they could very well be capable and well-minded, likely personally capable of coding. So let me give you another example in the same vein as C, where everybody uses a technology that is terrible, questioning it only at the outset, and then just…
Clarifying that what I mean by this is that it's not realistic to expect large C codebases to be perfect. Bug-free, with no exploits. Perfect. Same thing.