Not sure if this is meant as a joke an I'm making a fool of myself for even replying.
How would the file name (or extension in that case) have any impact on the content? A text file is not a CIA file. The file format is described here:
[3dbrew] CIA
Let me answer it that way:
I took a bunch of old cardboard boxes and a permanent marker and then wrote "High end laptop!" on each box. Why didn't this produce a bunch of expensive, working laptop computers I can sell for profit?
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What I can't answer – being not a developer – is if there are homebrew development tools – compiler or even an full IDE (integrated development environment) – for running directly on the 3DS. What I can say is that programming on the 3DS is not practical. The only thing I personally ever did in this regard was writing a small application visualizing a few sorting algorithms with minimalist graphics in SmileBasic. And even that became huge headache (tiny screen, no physical keyboard).
All in all SmileBasic is an officially produced 3DS application intended for programming your own games – with the BASIC interpreter pulling on nostalgic feelings… the memories of
QBASIC.EXE contained in later MS-DOS versions.
A game engine (physics, graphics, sound) is a VERY complex program of significant size.
Are you maybe thinking of some kind of game maker? A ready to use application allowing to essentially click together a game within the limits of this particular game maker?