Why did the Slam Dunk anime never adapt the National Tournament?

The facts first. Toei Animation's Slam Dunk ran on TV Asahi from October 16, 1993 to March 23, 1996, for 101 episodes. Wikipedia's summary of the adaptation is one plain sentence: the anime followed the manga storyline, but left out the National Tournament games. Shohoku qualifies for the Nationals, trains, says its goodbyes, and boards the train. The tournament itself, the part of the manga readers rate highest, was never animated for television.

The last episode shows what filled the space instead. Episode 101, "The Glorious Slam Dunk," aired on March 23, 1996 and closes a practice game against a combined team of Shoyo and Ryonan players, Shohoku winning 76 to 74 on a Sakuragi play, before the final scene sends Shohoku and Kainan off to the Inter High. The closing episodes, 97 to 101, are anime original material built around the manga's chapters 190 to 197. The National Tournament begins at chapter 198, in volume 22. From there to the final chapter 276, roughly the last nine volumes of the manga, television never went.

Now the gap, stated plainly. No official statement explaining the stop exists in the record opened for this page. Reporting on the question says the same thing: there was no official statement, and what circulates instead is fan theory. The theories are familiar: a dispute between Toei Animation and Inoue over the story's direction, ratings trouble, or budget trouble. None of them is supported by an on record statement from Toei, Shueisha, or Inoue in any source opened here, so none of them is printed on this page as a cause. They are the shape of a hole in the record, not an answer.

One timing fact is documented, and it is context, not a cause: the anime ended on March 23, 1996, almost three months before the manga itself ended on June 17, 1996. When television stopped, even the manga's own final game was still being published. The Nationals finally reached animation 26 years later, in the 2022 film The First Slam Dunk, and even then only the final match, against Sannoh, was filmed. The rest of the tournament, Toyotama and all, remains print only to this day.