The original deal was for three years, and NASCAR did it for those three years.
The attendance was not very good, lots of empty seats. And it cost a whole slew of money to put the race on for both the teams and NASCAR. The scheme had two goals, neither of which has been acheived.
First they hoped perhaps the interest would be high enough that a NASCAR type series could be started in Japan, it wasn't. They also hoped that perhaps a Japanese business or three might be lured into sponsorship for teams in the states. Except for the Kikkoman sponsorship of Hideo, which is limited, that hasn't really taken hold to my knowledge either.
The next step of bringing Toyota into the fold, might prove eventually to acheive both goals. We'll have to see.