Not all that strange.
Supporting MacOS after supporting iOS, is likely a fairly easy port (depending on specifics of their code). Shared code, same tools, same developers. On the other hand, supporting windows would require an entirely new app, likely sharing very little code, and requiring different developers.
Said another way, it was probably very cheap for them to support MacOS, and would be much more expensive to support windows.
Voice your requests to Lumin. It’s the only way to get it prioritized.