I'll tell you why. Nissan didn't know their ass from a hole in the ground back in the 90's. They couldn't run a business if they tried, which is why they went bankrupt later than decade. There was no reason to leave the SR or CA out of the S13 (or S14 for that matter). You're talking about a company who's Japanese line-up in 1996 contained 2 versions of the 180sx, 3 Silvia versions plus the 270R, 2 300ZXs, something like 8 Skyline versions, Turbo Bluebird, Turbo Avenir, Stagea, Cefiro, etc. You know what we got in 1996? non-turbo Z, 2 NA versions of the S14, and 400 turbo Z's. It is obvious that Nissan of Japan did not care about North America. I think that war and those 2 nukes 50 years earlier might have been effecting their plans.

And to address the bullet points above:
1. Of course the KA24E is cheaper than the CA18DET. There's no turbo, IC, coil on plug, etc. And the E's 140HP is no where near the 180ish that the CA makes.

2. Japan was not worried about canibalization. Just look at their Japanese model line up above.

3. The gas thing is wrong on 2 counts. Everyone who's ever stolen a "93" sticker knows that we use RON+MON/2. So, 93 RON is something like what we call 89. 98 RON is roughly the equivalent of our 93. Secondly, there was no rareity to premium fuels. My Dad had no problem putting 93 in his 87 Turbo Z every week from 1987 to 1998 over the course of 130k miles.

4. Spares pricing? Don't forget about spares from the B14 SE-R. The CA18DET is almost the same motor as the CA18DE in the Pulsar that we had. "spares" is a pretty weak argument.

In conclusion, I believe the reason that we never saw "the good stuff" was a mix of political reasons, Japan's lack of understanding about the American market, and Nissan's inability to run a business properly in that time period.

*edit*
<---- that's a humdinger of a 2000's post!