Yes, macOS and companion iOS are the real problem here. Together with the hardware they form an "ecosystem", which is conducive to getting things done, especially for people who need to juggle many responsibilities at once (think entrepreneurs/bootstrappers) and who really do not have time to deal with OS issues.

And please believe me that I did my homework before saying "no viable competitors". I regularly use Linux, Mac OS and Windows. It's not even close. I mean, seriously, Linux doesn't even have a sane concept of a system-wide clipboard. So in the end, hardware itself doesn't matter much, unless you mostly stare at it. If you want to use it to get work done, what matters is the entire package: hardware, OS, application software, companion devices.