It seems like it's linked to two things: a couple really awesome builders going away that made awesome, versatile builds good for a bunch of different play styles (ACM, Sirrus, and Ace all come to mind right away), and the disappearance of clans. Way back, there were major clans like USSR, and more recently, BAN and ARES (MARS attempting a revival, but it's not looking good), and those clans consistently released epic, playable builds. There are far fewer clans hanging around the forums now, and those that are tend to show off pictures as teasers while never releasing what they've made.
There are a few good ones still around: Height releases some of their stuff, even if they are a little overprotective of their build quality, and OceanCo definitely deserves some mention, since StarHawk goes out of his way not just to make his clan's builds open, but he also goes out of his way to offer building tips and feedback to make other people's builds better, which will make them more playable.