Confusing Dots

ps = Flatten[
   Table[
    {x, y, 0}
    , {x, -3, 3, 0.1}, {y, -3, 3, 0.1}],
   1];
Manipulate[
 W = ({
     {1, 2, 0},
     {-1, 1, 1}
    }).RotationMatrix[\[Theta], {0, 0, 1}];
 ps2d = ps.Transpose[W];
 Graphics[
  {Yellow, PointSize[Medium], Point[ps2d]}
  , Background -> RGBColor[0.1, 0.3, 0.15], PlotRange -> 3]
 , {\[Theta], 0, Pi/2}]