ARM is all over the place with its ISA. x86 has the benefit that most companies made it 'IBM compatible'. There are one off x86 ISAs but they are mostly forgotten at this point. The ARM CPU family itself is fairly consistent (mostly), but included hardware is a very mixed bag. The x86 has on the other hand the history of build it to make it work like IBM. All the way from how things boot up, memory space addresses, must have I/O, etc. ARM on the other hand may or may not have that depending on which ISA you target or are creating. Things like the raspberry PI has changed some of that as many are mimicking the broadcom ISA and specifically that with the raspberry pi one. The x86 arch has also picked up some interesting baggage along the way because of what it is. We can mostly ignore it but it is there. For example you would not build a ARM board these days with an IDE interface but some of those bits still exist in the x86 world.
ARM is more of a tool kit to build different purpose built computers (you even see them show up in usb sticks). While x86 is particular ISA that has a long history behind it. So you may see something like 'Amazon builds its own ARM computers'. That means they spun their own boards, built their own toolchains (more likely recompiled existing ones), and probably have their own OS distro to match. Each one of those is a fairly large endeavor to do. When you see something like 'Amazon builds its own x86 boards', they have shaved out the other two parts of that and are focusing on hardware. That they are building their own means they see the value in owning the whole stack. Also if you have your own distro means you usually have to 'own' building the whole thing. So I can go grab an x86 gcc stack from my repo provider. They will need to act as the repo owner and build it themselves and keep up with the patches. Depending on what has been added that can be quite the task all by itself.
ARM is more of a tool kit to build different purpose built computers (you even see them show up in usb sticks). While x86 is particular ISA that has a long history behind it. So you may see something like 'Amazon builds its own ARM computers'. That means they spun their own boards, built their own toolchains (more likely recompiled existing ones), and probably have their own OS distro to match. Each one of those is a fairly large endeavor to do. When you see something like 'Amazon builds its own x86 boards', they have shaved out the other two parts of that and are focusing on hardware. That they are building their own means they see the value in owning the whole stack. Also if you have your own distro means you usually have to 'own' building the whole thing. So I can go grab an x86 gcc stack from my repo provider. They will need to act as the repo owner and build it themselves and keep up with the patches. Depending on what has been added that can be quite the task all by itself.