Back in 2005, Crash Tag Team Racing was initially planned to be released on the Nintendo DS alongside the other console versions. Due to the console's inferior hardware, this version wasn't going to be a direct port, but it was meant to be as similar to the other versions as possible, and it was being developed by Sensory Sweep.
Despite being the first version publicly announced (back when the game was still being called Crash Clash Racing), no screenshots were ever released. Thanks to the efforts of a Crash Bandicoot fan nicknamed Bitmap, we finally got to see some images and information related to this version in 2014.
Sensory Sweep was initially sent the character models by Radical Entertainment and entrusted with the task of reducing several thousands of polygons to a few, mere hundreds. Since this robbed the characters of their detail and made them look boxy, the artist in charge of the character models instead opted for making his own models and textures from scratch based on the ones he was sent, which yielded much better results. The race tracks and their layouts were also based on those from the other versions.
The game was in development for 9 to 10 months before being cancelled, with only 1 or 2 months left until it was finished. Despite the smooth progress, Sensory Sweep was told by the publisher that the game was going to be cancelled, as Mario Kart DS was scheduled to come out at the same time, and the publisher didn't think it would sell as well as hoped with the direct competition.
While this was the "official" reason given by the publisher, there were rumors around the Sensory Sweep office that the publisher had some problems with their management. Sensory Sweep wasn't exactly the best run studio, so this is the most likely cause of the game's cancellation (you can find some stories about the studio's management out there, if you're curious).