May I ask why you think its Windows - only? OTA is usually available via an APP, phone-APP or any HTML5 I/face capability. Did I miss something ?While that would certainly be a powerful option, if it were offered I would also want the ability to do that with a Mac. It's annoying to have to dust off some old Windows machine just to run a piece of software. Many companies do it but IMO "Windows-only" is just as unnecessary and outdated as Android or iOS only.
I can guess that a couple of reasons why they are not are: 1) there is more that can go wrong when they don't control the entire sequence and allow the user/updater more access to the process. And 2) it massively opens up the system to reverse engineering and manipulation. While there is certainly some exposure with any user applied updates, attempting to retain reasonable control is understandable. Sure the current shop system is technically around, but there are legal and business motivations that are not present with end users.