Manjaro seems to have two main user groups: people switching from ubuntu/mint/other beginner distro and arch veterans who are tired of the long install process and just want an arch based system that works.
The newbies (and I say this from experience as I clearly remember being one myself) see things like the avahi and v4l2 utilities, as well as yakuake and gsmartcontrol (just as a few examples) and think of them as tools they will not use that are cluttering up their workspace, or utilities for more advanced users that may even go as far as to turn them away from manjaro thinking it it too advanced for them.
The arch migrants are also used to minimal distros where they install any software they wish to use themselves, so it would make sense to let them choose their own programs.
And also something I have observed for all operating systems, Linux or not, is that installing a program that is not included by default can be easily overlooked, however having to go through one’s device and remove applications that they do not want or use leaves a bad impression on users.
Well that is my opinion anyway, feel free to disregard it, although I feel it would help the growth and spread of Manjaro as a popular Linux distribution.