The nex format is for compiled software. The ones I produce are in NextBasic (.bas format).
I had a couple of reasons for creating BASIC software. One was a challenge to see whether the Basic and hardware features on the Next could perform well enough to produce decent games without resorting to machine code.
The second was because I wanted to also offer them as free code for people to play with, learn from or just enjoy the chance to look at how the game works (which is why I write the pdf guides). It brings back memories of the 80's era of home computing that I grew up in (but now on a *modern* 8-bit system)
And of course, because its just a lot of fun to write games... :)