The Design and Development of the 3.1.0 Gems

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Fire

One of the early doubts during discussions with other developers was the plan for everything to deal Fire damage. Originally, Unearth was also planned as a fire skill.

We have a few skill sets that have a diverse set of elements, like traps and elemental attacks. These do have the advantage of naturally creating a more diverse variety of builds within the skill set but often restrict players and their choices when the passive tree or item choices they take end up restricting their benefits to only one of the skills in the skill set. For example, building Lightning Trap could mean taking bonuses to Projectile effects and Lightning Damage, making it a painful process if the player later wants to try out Ice Trap.

This is something I've been curious for a while. Fire seems to be for some reason a special element in PoE, in that there are many unique fire-based skills which have no or very few counterparts for other elements.

All the corpse-based skills are fire.
All the channeling elemental skills (before 3.1 added Lightning Tendrils) are fire.
All the damage over time skills are fire or chaos.
All active totem skills are fire (Flame Totem, Searing Bond) or physical.
Righteous Fire does not really have any other equivalent.
Ignite Proliferation.
Added Fire Damage and Herald of Ash work differently than Added Cold/Lightning and Herald of Ice/Thunder.
Avatar of Fire is a thing, but there is no global conversion to any other element. (Yes I am aware that this is constrained by the conversion order.)

Meanwhile it seems that almost every cold/lightning skill has another skill that is very similar to it, of other elements.

Ice Shot / Lightning Arrow / Explosive Arrow.
Frost Blades / Lightning Strike / Molten Strike.
Ice Trap / Lightning Trap / Fire Trap.
Hypothermia / Innervate / Immolate.
All the Purities / Golems / Curses come in all three elemental variants.

The only skill that really stands out as being Cold-specific with no other equivalent is Frost Wall.

Is this a design decision? If so, what are the reasons behind it? I would like to see more Cold and Lightning skills which are unique on their own, not just "reskin of skill X dealing Cold damage instead".