Why can't you put insignias on Tyrian armor?

When insignias came out, they were in Tyria too, so I bought some, but I couldn't use them on my armor, because it's Tyrian. So I wonder why they even have insignias in Tyria. And would it really corrupt the game if you could put insignias on Tyrian armor? You should at least be able to if you own Nightfall, which I do.

Tyrian armour was created before Nightfall came out. With Nightfall a new armour system came out. The reason insignias dropped in Tyria is probably because "rune" drops are random. People have asked for the armour system to become universal ever since Factions came out, I really don't see it changing.

Insignias do NOT drop in Tyria or Cantha. The OP bought them from the rune trader.

Answer:
Because Proph and Factions armor comes with "bonuses" already on their armor (+10 versus ele for example)

Nightfall armor doesn't.
I assume they wanted to change it up.

One thing I mentioned to someone in game, when you're about to "buy" an insignia, there should be a pop up that says:
"Insignias are only useable on armor bought in Elona (Nightfall) and can't be used on armor bought in Tyria or Cantha. Are you sure you want to buy it?"

rune traders are "universal",meaning all the rune traders in all the chapters for all the servers share the same "stock". So they'll also offer insignia's in tyria and cantha, even though you cannot use them ...

making the new insignia armor system backwards compatible would be awesome ... but yeah, maybe a little warning pop-up from tyrian and canthan rune traders won't be that bad.

It is the same thing with Dye Traders and some of the Mecrhants offering the same goods.