There doesn't appear to be a goal of monetization as much as there is a goal of ubiquity through proliferation. If that were reversed there is no question that the GPL is a better choice.
I happen to think CPAL is exactly the right choice and here's why:
1. It's one of only 3 OSS licenses that take the "network" into account (CPAL, OSL, AGPL) whereby usage can be considered distribution.
2. It doesn't require that code be given back
3. It enforces the brand of the developer (in this case Reddit) which actually has some benefits.
Matt has been mostly against CPAL (see this post about Facebook) but I have been trying to sway him into realizing that the license doesn't dissuade developers. His argument (which makes sense to a point) is that they should put code out under Apache or something completely permissive. That however, limits what the code developer themselves might want to do in the future.