To make it quick and dirty - I'm a newb programmer who's looking hard at Pyglet, it looks like a really clean and friendly module to use, unlike something like PyGame which is, even by looking with my own inexperienced eyes, a beast.
However.  PyGame is constantly being used, updated, reused by lots of people and seems to have quite a following.  Pyglet hasn't been updated since January 2010.  Most works of art are never finished, only abandoned - but two years and it's still on v 1.1.4 seems troubling.
So while I might be specifically asking about Pyglet vs. PyGame, I'm also not, because it leads me wonder about other ghostly modules that might be lurking out there, that had promise once upon a time but, for some reason, got dropped or shoved in a corner and aren't really relevant.  Are such abandoned projects not worth the time and brain-space investment?
To paraphrase Monty Python

No no he's not stagnant, he's, he's restin'!

Open source maintainers move on or get busy with other things.  If you feel Pyglet is a good choice for your application create a clone of the repo, put your changes up on insert code hosting flavor of the month, and get some work done.  There are benefits to having a community to ask for help or fix bugs.
However, if something is open source and a good fit for your project the lack of a maintainer should be seen as an opportunity and not a problem.
Python - Is it worthwhile to invest time in apparently stagnant modules?