Before you ask why, pause to consider, as did Robert F. Kennedy (by way of George Bernard Shaw) "why not"? Windows 95 is still a perfectly fine operating system, and the New Nintendo 3DS, with its 268 MHz processor (and 256 MB of RAM) is shades more powerful than anything that could operate this top-of-the-line system when it launched 20 years ago.
Now, what can a New Nintendo 3DS with Windows 95 do? A bunch of folks are fulminating about emulating PC games and such, but that's really not the point. The point is someone, like the earliest explorers contemplating the tallest mountains, set out to put Windows 95 on a New Nintendo 3DS because it is there.
And they did. 2016 is off to a glorious start full of possibility and excitement.