Say what now? Do you own a 2DS? Have you used a 2DS? You evidently don't know what one is, so I'll tell you: it's a 3DS without the 3D or the clamshell design, aimed at children or those on a lower budget. I have one and it's excellent.
I myself use a 2DS. It functions very much as normal albeit bulkier. The reason I buy one is because I was financially unstable and just needed a machine for Pokemon.
Like what 09philj said, its directed for children whose budget is lower compared to adults or old teens. Also, it was released closely alongside the release of the Pokemon games so that players have a less expensive option if they just wanted to play the specific game. (I'm an example)
I really want to hear arguments from you why the 2DS is a fail, and like philj, I really want to know if you actually used a 2DS or even own one to make such statements like this.
Also if we're talking about the 'dumbest gaming fails ever' then let me bring up the Virtual Boy. And yes, they specifically made for it to be mobile. Could you imagine walking around with that thing on?
Game Theory did a good episode about why the virtual boy was a failure. Largely, it was because most of the effort was going into the next "regular" console.