No big secret in this. The reason why it has less users is the same why rolling release distributions have less users in general. The users are expected to have deep knowledge of how the system works and fix the problems, when there is one, on their own. This is not the profile of most of the Linux users I have met in the last decade. Another point that scare new users is its command line installation. I personally like it because I have total control over what is installed or not. But not everyone likes this kind of installation, and I understand their reasons.
I prefer Arch over the distros listed as supported exactly because of its rolling release model. Install once and from this point on you will always have the latest version of every software whenever you do an update. No need to wait for 6 or 12 months as in most distros (I have been using plasma-next as my desktop for quite some time for example)… A direct consequence of this approach is that the number of programs in its repository is larger than in almost all other distros I have tried (the advantage of not having to start a repository from scratch every 6 or 12 months). And I have tried many along the years. Probably only debian sid has more packages, and even in it I could not find some of the programs I have in Arch repositories.
I agree that a dual boot would be a more appropriated solution on the long run. And I would probably be doing this if the problem could not be solved using a LTS kernel.