Drivers. Another issue is the variety of distros. While it's essential to have that variety for power users like yourself, n00bs are confused and hopelessly. Mint is a good effort to resolve that, but is hamstrung by the lack of a defined ecosystem IMHO. It's not an issue for Apple, and M$ is less complex, given the deprecation of earlier releases.
Syncing is powerful, but I don't do it at all. Unless it is controlled by the user, the data retention in the cloud is an unacceptable security risk. Most folks have no issue with it, and loonix makes it easier to run a server that handles that in house for them as do, but that's not n00bs.
TBQH, I think the third leg of the Linux ecosystem is open source hardware, which is coming slowly, but coming.
Thanks!