The entire industry is intent on pushing builders upscale. Garmin? Dynon, AFS, GRT, etc... They, and Van's, and the rest of the industry know that you'll spend 5x the $$ on the panel and accessories for an RV-X than you'll spend for the panel on a Pietenpol. Same thing with the engine... Lycoming loves high end EAB's. So does Hartzell. They are glad to sell to the Piet or Fly-Baby builder, but the real money is in higher end stuff. So they push you in that direction. The plans only airplanes basically only exist in the little bitty AD's in the back of SA. You won't see a huge Hatz booth at Oshkosh. Fly Baby or Piet either. So those designs don't even register with today's 30 year old who becomes interested in building an airplane.
Directionally, Sport Aviation does the same thing. With few exceptions, which aircraft are featured? The expensive ones with professional panels, builder assist, and a $15k pro paint job. Right or wrong it is easy to believe that the EAA is happy to push the homebuilt fleet up market. EAA makes money off of the big vendors, whether in SA advertisements, booth space at Oshkosh, or in corporate donations. EAA wants those high dollar vendors happy and participating because that makes money for EAA.
So.. Short version: Marketing.
And now I'll go back to sanding on the RV-10 in the basement...