Now, that isn't to say there aren't security issues, nor that QA is perfect on devices they do support (like with any enterprise software projects), but it is a valid reason from a business perspective to not support everything.
Why do you think generally OpenBSD and such platforms aren't supported by commercial software, nor most open-source software? It adds a lot of burden for testing and QA on developers who will need to become intricately familiar with yet another platform.
People stare blindly at some customer support answers and hinge everything on those words, but if you think carefully about how software, compatibility and support work, this all makes perfect sense.