Question on early Human magic usage

So I was reading through the Warcraft Chronicle and something struck me as a bit odd.

After the High Elves founded Silvermoon, they crafted Runestones that would prevent their magic usage from being detected by the Burning Legion.

However, after Dalaran came to them for help when Demons started popping up, they did not offer this same solution for the humans.

Does anyone know why this is? Did the High Elves just want to use the Demonic encroachment as a means of trying to get humans to stop using magic? Had the method of creating these Runestones been forgotten over time?