To understand why "GTA SA Nintendo DS" isn't a retail reality, one has to look at the hardware. The Nintendo DS, released in 2004, was a revolutionary handheld, but it was significantly less powerful than the PlayStation 2 hardware San Andreas was built for.

These projects usually feature a low-poly version of CJ and a small block of Los Santos. They serve as "proofs of concept" rather than playable games, pushing the DS hardware to its absolute limit with custom textures and simplified physics. 4. Legacy: The Spirit of San Andreas on Nintendo

Now, look at the Nintendo DS. Released in 2004, the DS cartridges (at launch) maxed out at 128 MB. The DS had 4 MB of RAM and a 67 MHz processor. To put it bluntly: San Andreas would have exploded a DS.