Covering different uses, even though there is a bit of overlap. There's training and inference for ML models. CoreML can only do inference, but it's available everywhere. So if I'm an engineer on Apple Music that wants to pull out the dominant colors of album art for the background gradient of the player view on iOS/tvOS/etc, CoreML is what I need to use, feeding it a pre-trained model ready to use for inference. MLX is based on APIs that data scientists already use with other frameworks for training and inference. MLX is very much going to be macOS-focused because of the training aspect of it, which includes the python bindings as python has become very popular for data science. But what it means is that I can use MLX to get good performance to train that ML model that pulls out the dominant colors in an image on my MacBook Pro and save time.
The bolded bit is important. The biggest failing of Windows 8 (IMO) as an ARM platform was the ability to recompile an existing app for it. You had to use .NET and the "modern" touch-based UI for ARM. You could use the C++ bindings on .NET, but it wasn't like you could bring Photoshop to the Surface RT tablet at all. It was trying to make Windows into an iPad competitor, and failed to get the needed traction even for that, let alone laptops that wanted the full Windows UI.