Because it would require much more precision in heating and cooling, which would be annoying.
Also:
BudCharles:
Fear of breaking saves probably.
OFC it works well.. portals have channels nowadays..
Ah, but the thing I found is that the portal-in "swallows" the spark, unlike WIFI.
I suggested wifi temp 0~9700 for tmp1, tpm2, tpm3 etc.
so we would have MUCH more channels. I agree we need it.
I was thinking another thing.. I didn't know that portals actually transfer sprk.. and that's supposed to happen. Metal lines and metal lines with sprk jumping gaps have the same speed.. it's like those gaps had metal in them.
That can easily be worked around
Portals have exceptions though, as you can see. WIFI acts more as a signal, where portals, like @ThunderSt said, "swallow" up the metal itself in a way. It also cuts off the circuit, if you get what I mean. You have to add more wires around it to carry on.