That was the point! They were supposed to look like a society who was putting more design and artistry into the ships, vehicles, architecture, etc. Once the Emperor takes control that goes down the tubes like the Dark Ages. Some rich Imperial worlds may have continued this trend in some ways so you might see fancier stuff there. So if you go to Coruscant you may see the same fancy personal speeders and things. The rest of the galaxy was just trying to get by without, as Obi Wan put it, any Imperial entanglements.
We talked in another thread about why we aren't seeing more Republic era stuff, military at least. My guess is that the Emperor had everything tightly controlled so they weren't going to lose a Star Destroyer or anything that would give the resistance a hand. We did see a Juggernaut (aka Turbotank... sigh...) in Rogue One in use on that prison planet. I'm thinking that they kept some older ships like Acclamators or Venators for patrolling systems on the borders. I would like to see a future OT era show have a Republic Gunship in use or maybe some clone trooper armor on the Rebels.
But I agree, scavenged equipment would seem only natural in the hands of the rebels.
