One word: Support
There is not much aftermarket support for the SR20DET here in the US because it is a Japanese engine. Japanese engines need Japanese parts that come from Japan <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/eh.gif" border="0" valign="absmiddle" alt=':eh:'> . The same for the KA, it is not considered a race engine or whatever, worthy to tune. I don't even know if it is available overseas. It most likely is, but because of the distinction of the SR, it is overshadowed. And unlike the SR, it is not built in the aspect of it to handle turbo, even tho it can.
Even tho there aren't that much high-powered SR's here, there are plenty in Japan.