They do have brands, but in a different way that you want/expect.
Why did it change from Gameboy to DS? That was a big hardware transition. The Gameboy, Gameboy Colour, Gameboy Pocket, Gameboy Advance, Gameboy SP and Gameboy Micro are all under the same hardware brand, based on being in the same generation, having similar architecture and playing the same kinds of games.
The DS, DS Lite, DSi, and DSi XL signified that this is no longer related to the previous handheld brand, but is instead a new one. All the handhelds within that brand are related by being in the same generation, having similar architecture and playing the same kinds of games.
Then the 3DS, 3DS XL and 2DS came along and....you get the idea.








