You'd have a point if it weren't for the fact that the Amazons' entire lifestyle revolves around war. In terms of aging, they're immortal, and most of them spend their days training for battle. If they were a mostly agrarian society, focusing on growing crops and stuff like learning and philosophy, you'd be spot on, but they're not. They're always preparing for war. That being the case, they would greatly benefit from more advanced weapons. I mean, considering what an Amazon can do with a bow and arrow, consider what they could do with an energy weapon that doesn't require reloading after avery shot. Their lack of advancement is incongruous with the rest of the DC universe. The Atlanteans are mostly peaceful among themselves (the events of Aquaman nonwithstanding), but they still advanced a bunch of their tech, not just weapons. Amazon society stood still in all respects.