If you bind devotion skill to Curse of Frailty it procs every second. But Curse of Frailty has no “every second” element, it is just a debuff with Duration, no damage no “for x seconds”.
What is the logic here? Does every debuff prccs with “nothing” once per second?
The logic is that everything curse-like skill with duration is applied each second within its duration. This mechanics makes them a really good proc machines.
Got it, I though this is only for damage of “x seconds: … for y seconds”. Was surprised that Curse of Frailty works, thought it one for the first cast.
Surprisingly, this is an opposite thing 
DoT can activate devotion only on the first tick. So, you should distinguish skills with DoTs from skills that are re-applied each second. For example, if you cast Ring of Steel skill from Nightblade mastery with taken improvement Circle of Slaughter, then only the first hit has a chance to activate bound devotion.