As mentioned before, pre-Crisis Amazons watched the world through a magic mirror.
However, let's look at current Amazons:
- At least three times a century the raid ships for sex. This gives them access to 'snapshots' of technology through the ages for them to tinker with, learn to understand, and make their own improvements/modifications to. Electricity, engines, phones, radios, guns, computers - these are the common things they would have come across in the last century alone.
- Hippolyta made reference to a young Diana of going to the outside world to 'make a weekend of it.' Apparently the Amazons are quite capable of coming and going as they please, or at least Hippolyta is. There is no reason, especially in light of discoveries from the sex raids, that Amazons shouldn't scout/raid for new technology.
- The Amazons still guard Doom's Doorway and believe that men are the enemy. That they know the 'musk of men' means they've encountered them before. Therefore they have every reason to keep up with any technology that can be used in warfare. Weapons, armor, antibiotics/surgical techniques, and communications come to mind.
- The Amazons trade for weapons with Hephaestus who has been shown to make modern weaponry (that Diana shuns in favor of a sword) Again, there is no logical reason why women who have to do battle with monsters from Tartarus would prefer a bow to an automatic weapon or a grenade. All we have seen of them is that they are warriors, and it's extremely logical for warriors to want to be the best at war.
- Those sex raids would also have given them insights into modern culture - photographs, art, novels, sculpture. We have seen no sign of any artistry on Themyscira, which means we have no creative Amazons or that no Amazon ever grew to appreciate art? Also nonsense given 3000 years of isolation (boredom) coupled with glimpses into a world that is full of these things, not to mention that there was art in Greece/the outside world when they went into seclusion.
- Given that they are visited by the gods and are magically immortal, DC could have gone with the enlightened magical society as pre-Flashpoint with fantastical monsters and magical weapons and other objects at their command.
It seems to me that the only reason they are barbaric and backwards is because Azzarello's story required them to be barbaric and backwards. There are, within the context of the new universe he created, plenty of reasons and opportunities for the Amazons to have advanced technologically, culturally and magically.
In a world where a man can become a top surgeon in five minutes by reading a library of medical texts, a race of super intelligent telepathic gorillas are hidden in the heart of Africa, a race of people makes magical and technological advances while isolated at the bottom of the ocean, and a man in his late 20s has mastered every martial art known to man while becoming a master of forensics, criminology, chemistry and a plethora of other skills while running a Fortune 500 company while spending nights running around the city in a bat suit? 'Makes no sense' just doesn't apply