why can't mazda just make an "sti" of a "wrx"?
God, for hundreds of reasons. You can fantasize all you want, but cars need to be made in the real world. With real world concerns. And real world limitations. And real world compromises made to bring products to market.
Right now is not a good time for excessive research and R&D when they already have a winning formula with this car. You can't just slap a new tranny and a rear end on a vehicle and say "TADA, RELIABLE AWD SYSTEM!" You need to find room for the rear drive shaft, retest the vehicle handling and readjust suspension, rework the ECU and the additional electronics you'll need to manage power in an AWD setup, and a whole laundry list of other things. And the costs will be passed on to us, the consumer.
Can they do it? Yes. Will they? Right now
why bother other than to feed some childish fantasy on a message board? The current car is winning awards and magazine comparisons, forcing other automakers to respond to its presence in the marketplace, and most importantly, selling well. If they price themselves out of the market segment they are winning right now, they may not have a winning formula anymore. It's not worth the risk right now, and frankly I don't know that it ever would be. Incremental improvement in successful vehicles is how branding and identity are established for a vehicle, which is why 30 years after they were introduced the Civic and the Corolla still sell well and have a reputation for fuel economy and reliability and quality. Mazda taking steps to try and do the same with the Mazda3 is
an intelligent thing to do. The Mazdaspeed3 is no different. We'll see a moonroof option, a bit of added weight (unfortunately), a small 5 HP increase which probably means a slightly fatter torque curve and a small improvement in power dropoff up around 6000rpm, some suspension and brake work (maybe). Another step down the right path.
Plus, competing with the STI and Evo market segment is not something a company without the same WRC pedigree like Mazda really wants to do right now. You throw the same half-assed AWD setup the Mazdaspeed6 had in the Mazdaspeed3 then line it up against two of the most technologically advanced AWD vehicles on the market with the sort of reputation those vehicles have and
you will get killed. Or you pay out the ass to develop a new, good AWD system and push vehicle costs through the roof. Neither idea is smart, neither idea is likely.
If for some reason Mazda does do that, it won't be any time soon given how everyone is bleeding money and showing sales decreases. Maybe in a few years if markets bounce back we'll see a Mazdaspeed3 GTX, who knows? Anyone worried about it happening
now or even any time soon is crazy.