I think as jeffbee said below it's not even the custom ARM cores, but rather Apple's ability to control not only the hardware but the software on-top of it. In a typical Windows machine you are dealing with your CPU and microcode made by AMD/Intel/Other, then the BIOS/Driver code written by your motherboard manufacturer, and your GPU from either the on-board, or dGPU from Intel/Nvidia/AMD and then Windows made by Microsoft. All of this leads to silly things like the ASUS ACPI driver bug [1] or Dell [2]. Apple does not suffer from this lack of control and communication, instead allowing tight integration.

[1]: https://github.com/Zephkek/Asus-ROG-Aml-Deep-Dive

[2]: https://triangulatedexistence.mataroa.blog/blog/i-uncovered-...