Well, barren and especially boring is a subjective term, I admit that. I think that black rock and green go design is boring by now.
But yeah, the entire thing is controlled by the legion. ~20k years ago Argus was home of the advanced civilization of the Eredar, ruled by Velen and Kil'Jaeden (and later also Archimonde). Eventually Sargeras approached them to join his ranks. He offered power, he wanted intelligent generals to lead his troops. Kil'Jaeden and Archimonde accepted, Velen did not. I would expect for Argus to change once most of it's inhabitants had been turned into demons, sure, but I would also expect the Eredar to keep their civilization intact. For many reasons, vanity, pride, quality of life... simply the fact that you can plan a war very well from an organized metropolis and less so from an obsidian waste. Also the Eredar we see in WoW are mostly dressed in fine garment with pattern. I find it hard to believe to go the extra length to present themselves in a civilized manner if they were not interested in living a civilized life.
Also there is little to gain from scrapping Argus. The legion has probably thousands to millions of planets. One more planet would not change the amount of resources by a lot. Millionaires who made their money from fracking usually don't do it in their own back yard.
They retconned so much to make Sargeras of all people more reasonable. But the Eredar, a race defined by their culture and intelligence are now pretty much stripped of their identity. Had Argus still been the paradise it was before they did the pact with Sargeras you could somehow relate to them more as villains. Demonic pacts are interesting because your side of the bargain is tempting. Eredar now are one dimensional and evil for evils sake. That is not very good story telling.
I don't want to put factions there and act like they have been there for millienia. I want to see the civilization that HAS been there for millennia.
Somehow the new location is both: "Way cooler" and "too boring to have more than one zone of"
I hope it is the first, I suspect it is the latter.