I myself have chimed in in the past to similar threads like these and there's always the same old excuse of "The car has only been out about a year probably less". Buck for buck the FRS/BRZ may not make as much power, but will always out perform the VT. The twins are even faster than the VT stock for stock right out of the box whether you're looking at a road course, autox, or drag race. VT loses in every single category except tech. FRS/BRZ weren't made for tech junkies. Everyone knows a fast car is a light one. What's the point of having a 400+ whp car when it also weighs nearly 4000 lbs? The point is to have 400+ whp at under 3000 lbs, you tell me which is a faster car.
Also just because it's a Subaru boxer engine does not mean it's the same as every other Subaru boxer engine out there. The one in the FRS/BRZ is the FA20 which is not the same as the EJ series engine found in the WRX's and Imprezas, so no it did not already have aftermarket parts. It came out the same time as the VT. Even before the car went on the sales floor across the nation, the car had turbo kits, basic bolt-ons, suspension mods from lowering springs to coilovers, etc etc...the list goes on.
However, I do agree with you that we have been lucky to have the few vendors that are spending their time to make us awesome parts. The FRS/BRZ were aimed for the tuner market, the VT was aimed for a diverse crowd whether you needed something a little stronger/faster and had the capacity to carry groceries, kids/passengers, and travel luggage. Then yet, could still be modified to perform and look better than stock. I contradict myself here, but this is where everyone gets confused as to why one car has more support than another. I WISH there was a full aftermarket backing for the VT, but the market isn't there. Out of hundreds or thousands of VT owners currently, how many of us actually upgrade our cars(I'm sorry, but this may offend some people but I DO NOT CONSIDER window tints, LED interior, exterior add-ons, plasti-dip, badge removal, etc as an upgrade)? The usual group buys I see are only around 10-20 buyers and that's about 1 or 2% of VT owners only, there's not much money to be made.