The most common argument for introducing YAPL goes like this:
"There are way too many programming languages out there. And they are each flawed in some way (small and odd, or large and incomprehensible). So I, in my wisdom and will create YAPL, which will displace all these other, inferior PL."
Of course the vast majority of other PLs were created for very similar reasons. There are two other motivations common in creating programming languages.
- An experiment: "Let's try this and see what happens."
- Scratching an itch: "I have a problem that's too hard to address with the tools at hand."
The latter often get over-sold on the assumption that everyone else "ought" to have the same itch. But sometimes these work. The former sometimes take off to the astonishment of the originators. The first kind of new language mentioned, the "new, better solution", takes continual pushing up-hill to get it adopted, as it often solves a problem the originator thinks other people have, in a way that the originator believes others should find useful.
Aside from that, yet another programming language is a fine idea. Especially one that's verbose, inconsistent, and probably incomplete without some kind of big magic.