They don't exist in the Alpha Quadrant. Doesn't mean it doesn't exist elsewhere. Plus, it was supposed to stop telekinetics from Eris, though it was fake. Telekinesis and telepathy are two different things.
Actually, I misremembered here: Quark specifically speaks of the device being a "telepathic suppressor", thus implicitly equating at least these two psi-abilities and probably many more as well - but he says he
has seen telepathic suppressors before, only much bulkier than this collar.
The bit about no telepathy blockers is at Memory Alpha implicitly attributed to TNG "Violations", where our heroes are at loss of ways to stop a telepathic criminal from practicing his art:
LaForge: "If one of them is behind this, will keeping telepaths in their quarters prevent it from happening again?"
Picard: "What else can we do? Station a guard? Set up a force field? I don't see that those would be any more effective."
But there might be Reasons why our Starfleet heroes do no consider applying technology that Quark is familiar with... They also tellingly do not consider assigning a Starfleet telepath to monitor the suspects, say.
Besides, given she was the only Vorta we saw who had that ability, I have to wonder if it was technology based and a device that was on her, or implanted. If the Founders could engineer telekinetic people, they wouldn't need the Jem'Hadar's weapons.
The other possibility is that the Vorta all do have this ability - it just sees no use because the Jem'Hadar do have guns, and other Vorta either are surrounded by gunmen (loyal or otherwise; it would do no good to start coughing out these balls of fire if the enemy can then gun you down in seconds), or injured.
The Founders deliberately engineer inferior servant species, that much we already know: for a couple of examples, the Vorta have dull senses even if sharp ones might seem advantageous, and the Jem'Hadar are not just addicts but also incapable of remaining invisible when actually fighting. But the motivation for leaving out the telekinesis gun from the Jem'Hadar could be different, too: it may directly tap into their already limited strength, just like cloaking, while a power clip for a handheld gun doesn't suffer from this.
Indeed, Jem'Hadar invisibility is apparently a "telepathic" skill much like the Vorta telekinesis. It takes concentration and strength. And the way it can flexibly hide from view not just the trooper but his equipment and clothing as well is nicely explained if it's a "Look elsewhere, nothing to see here" telepathic suggestion rather than some sort of a fancy forcefield.
I wonder if Betazoid telepathy
a) is tiring, physically and mentally, beyond the aspect of all that mental chitter-chatter being tiresome to listen to
b) also manifests as other psi-skills such as the ability to become unnoticeable or to open zippers without hands or light up cigarettes
?
Timo Saloniemi