The contradiction is the words stable vs unstable.
In reality the only difference between unstable and stable is the time taken when the core team decides to do the snap.
And because of that updates are much more frequent on unstable and as such much less prone to weird - hard to find issues - because you have a fairly short log of what happened and the troubleshooting process - in case of accidents - is much easier to handle.
The users using unstable are known capable and informed and able to fix small issues in a snap while many users on stable are #newbies - so when the packages are snapped to stable - the #newbies who have filled their system with interesting and 'useful' packages build from AUR - clicks the update icon and because there - most likely - is updates to kernels, drivers and x - the whole #! becomes unresponsive - user forcefully restart and the song begin.
without knowing that adding them adds a boatload of possible conflicts and required rebuilds -