[Spoilers All] Dwarves and Archdemons

I agree that it's a recent note. I wrote an answer to the rest of your post. I apologize. It got long, fast.

Here's my reasoning on why it took them so long to act.

In Inquisition, it's greatly implied that a serious army is needed to even just reach the gods. Going off of this, the Wardens didn't hunt out the sleeping gods in the past because they didn't have the numbers it took to venture into what are likely unknown swaths of the Deep Roads in search of the gods.

They're likely going to be entrenched for a long, indeterminate period of time. It's unlikely that they have any idea how much of the Deep Roads are intact around the resting place of the god. This means that they're going to need basic manual labor at the least. More realistically, they're going to need people that know what they're doing with underground construction. Tunnels will have to be cleared, or new ones dug in their place, and stabilized. There's enough danger in the Deep Roads already. They can't be making it that much harder on themselves with being careless clearing the way. That all means that they're going to need a large workforce as well as several experts when it comes to dwarven architecture. These workers will need protection.

Which is the second major area of concern. It will be very hard to know how many darkspawn to anticipate being in the area. Yes, the Wardens can sense them, but it's not doing them much good just in the theorizing and planning stages. Even scouting runs will only help so much. Has a Warden in the past has gotten close to a sleeping god and recorded how the darkspawn move in the area around it? Will non-darkspawn digging in the area draw more darkspawn than that past Warden observed? Likely. Will it aggravate them? Probably. Are they going to lose men and more importantly, women to them? Definitely, which means more broodmothers which means fast, easy reinforcements for the darkspawn. How do you prevent against this? Not take women with you? That's going to cut down on your precious numbers.

With those two major areas considered, they're looking at a situation where they're going to possibly need a large workforce (diggers) and a large fighting force for protecting those diggers, as the chance of them being under constant attack seems to be high. They'll also be deep below ground and need to secure supply routes back up to the surface, which further complicates matters. The Wardens have simply never had the numbers to accomplish this feat. So it was never attempted in any meaningful way.

Also, what if, in their attempts to reach the god(s), they fail, falling to the darkspawn? Congratulations, you just made it stupendously easy for the darkspawn to finish your digging and start a new Blight.

So, they decide never to pursue the Old Gods before now. When Corypheus and his false Calling come along, they panic and think that what most everyone believes is the entire world's only means for surviving the future Blights may cease to exist in the very, very near future. Then comes Erimond, offering them a way to make a powerful army, quickly. Exactly what they need.

TL;DR: The Wardens never pursued the Old Gods before Corypheus popped up because the logistics involved and the risk of failure are staggering.

/r/dragonage Thread Parent