The computer models may differ in performance, reliability or some other characteristic.
Very rarely is a compiled software compatible with multiple different CPU architectures.
[1] Hardware that is compatible may not always run at its highest stated performance, but it can nevertheless work with legacy components.
[2] Hardware that was designed for one operating system may not work for another, if device or kernel drivers are unavailable.
This is often due to manufacturers obstructing FOSS such as by not disclosing the interfaces or other specifications needed for members of the FOSS movement to write drivers for their hardware - for instance as they wish customers to run only their own proprietary software or as they might benefit from partnerships.