Curious about some sigils

Hi all,

I am curious about something rather simple. There are several sigils that inflict conditions, for example there is Sigil of Earth, inflict 1 stacks of bleeding on crit, then there is sigil of torment which inflicts 2 stacks of torment (not only for your target, but for all enemies, this one seems better) on crit, etc. Now, there is none for burning or confusion.

So, I am curious as of why. Anyone knows anything about it? Has the devs over the year said something, do you have any theories?

Also, Aegis/Protection/Resistance/Resolution sigil when? xD

NOTE1: Yes, I kinda assume it is because of balance, but I see no reason to not have, lets say, a burning sigil with a combination of less stacks/less duration/higher cooldown and balancing it with the other options.

EDIT: corrected bleeding stack count and added note 1.