Well, some people don't want to pay the money for such little to no gain. But for the SVT Focus, most of the parts are for drivability not power gain.
Meaning, each upgrade it helps the car move easier and reach it's power band quicker as well. Better throttle response from an upgraded TB is one of them.
The only N/A bolt on that really gains you across the powerboard are the upgraded Cats. The ORP or HFC.