Because they don't have a free stand alone computer in their car. The mazda computer may be an EEC but the strategy is yet to cracked. I can make any car run great WOT most of the time with bolt on parts, but a truly good tune will run like factory all the time and will be safe. NO check engine lights unless their is a problem is a wonderful thing. It also helps with emissions if that is an issue. There is also a feature in your EEC called aircharge WOT multiplier. What is does is monitors air flow and if it gets too high the EEC freaks out. You also have some emission switches like cat temp flange sensor that will dump fuel like mad in WOT to compensate for Cat temperature. There is neutral and decel idle air control so no stall issue. Also dashpot decay rate that will control the engine flare between shifts if it becomes a problem. The list goes on and on but you will be better off with a tune. I'd have to pull up your ECU code to know specifically what you have. They are all different. I charge $425 for a FI tune including dyno time and the chip out here in Phoenix. I know I'm on the cheap side so expect to find prices between that and $700 on the high side.
