That's mental. Was Apple party to the decision for Acorn to spin its evolving RISC architecture into its own company? Yes. Were Apple responsible? No. Apple's interest in RISC/ARM-driven CPUs can be mapped to 1992 (the Newton) then zip until fifteen years later (iPhone). Unless you wish to count the über low-powered ARM microcontrollers included in iPods. That's a stretch given the iPod wasn't a software platform.
In what way have Microsoft, Intel, Google or Amazon tried to replicate Apple going all-in on building their own software on their own hardware?
Microsoft have their own OS but have never tried optimising their own OS/software for their custom own CPU/GPU architecture. Intel don't have their own OS. Google's plan for Android was not that it wouldn't be tailored for their own specific hardware but that it would run on a wide variety of hardware. Amazon neither have their own OS, nor their own CPU or even their own hardware.
Why hasn't Microsoft invested fully into a vertically integrated system for general computing, whereas they have for games (Xbox)? Who the hell knows. Developing and gaining traction for a new OS looks to me to be the biggest barrier. Taking the ARM IP and tailoring that for your OS, software and hardware looks like the least amount of effort. Apple have chopped-and-changed CPU architectures three times now (680x0, PowerPC, Intel, ARM). Done right, it doesn't present any kind of barrier.