courtesy of Silky Venom
Presence
The continental effect is removed by certain resonating catalysts.
The logic behind this is a bit weird: resonating enhancement with a proc, such as "of might", remove the continental effect from armor, while only the health and energy catalysts remove it from weapons and all other procs, like for example striking or soulsip, keeps it.
Resonating catalysts that do not add any proc, like for example of accuracy, do not remove the continental effect. Focusing catalysts never add a proc and never remove the continental effect.
Popularity
On highlevel, the most important continental effect is the thestran one, because a player who wields only thestran items in all his 18 adventuring gear slots (other than mask, which cannot be crafted, and ammo case, which doesnt get a continental effect even if crafted), gets a whooping 18% on accuracy.
Compared to that, a player in all kojani would get 54 damage on every attack (thats quite something, but not as much as it sound, as its a flat increase and not actually something multiplied by crits).
A player in all qalian would only get a heal effect that can, on that level, only be called perfectly microscopic (about 15 or so if the character is a healer in with maxed Vit and healing focus) and is pretty small already on lowlevel.
History
Boon of Health with Qalian Gear
Qalian effects have been much more popular in the past. The reason was rather simple: classes that can not heal themselves, such as Warrior, or which arent very good at it, namely Ranger, could wear some qalian gear and some items with the Boon of Health, created by the 'of Health' catalyst, on them. The Boon of Health would strengthen the minimal healing of the qalian continental effect, to the degree of making it actually noticeable.
Starting with Tier 3, thanks to focusing catalysts, very piece of this gear could even have something nice on it, even if only halfed in power.
Lets assume the character in question is a ranger with two really fast and powerful weapons, qalian daggers of striking, a full set of qalian jewelry with +Wis (qalian jewelry can only have +Int or +Wis), and a bow and cloak which are again qalian. So this is 9 items all triggering the heal with a 15% chance, for an average of 1.35 heals per attack, on a very fast weapon that is dualwielded. The armor is fully set to Boon of Health, so that is 9 times a bonus of 10 on the base heal, which might be something like 5 for a ranger (how high it is depends upon the Vitality and Healnig Focus of the character). The average heal per attack is the 1.35 * 95 = 125.25. A quick check reveals that one piece of armor should even be without the Boon of Health, because then the average healing is even higher: 1.5 * 85 = 127.5. A second piece however is a bad idea, then the healing drops to 1.65 * 75 = 123.75. So 10 items triggering 8 Boon of Health is the optimum.
And thats what the devs didnt liked to see, so they made Boon of Health not working on the continental effect. Ever since, Qalian has turned very unpopular for gear.