I'm not sure I understand the question. What is meant by "Why do NWN modders avoid NWN2?" How is is that we are supposed to be "avoiding" NWN2?
Does the question mean, why do we still mod for NWN instead of modding for NWN2? If we did, then wouldn't we no longer be NWN modders? In that case, doesn't the question become, why haven't we abandoned NWN in favor of NWN2? It comes across as just a bit less friendly when phrased in that way.
Now, if the intention is to ask, why is it that some in the NWN community are as hostile as they are toward NWN2, then that's another (and at least more reasonable) question. Since I emphatically don't share that hostility, I'll have to leave it to others who do to comment on. Speaking as a NWN modder, however, the reasons I never switched to NWN2 are as follows.
1) I started my project in NWN1, and changing engines between chapters was a problematic proposition at best. (I floated the idea a number of times, and it was met with considerable hostility on the part of my player base.) My interest in modding was to develop that project, and I had no desire to start a new one just to be able to mod for a new game.
2) At the time when I could have considered switching (circa 2007), NWN2 was still too unstable and not mature enough as a platform to do so. It was also extremely impoverished with regard to custom content development, for several reasons (including that it was new, and that NWN2's Granny based design made it very difficult to develop). Since I felt that the project I was working on needed a decent variety of custom content to be done right, I chose to continue working in NWN.
3) Development in NWN is faster and easier than in NWN2 (especially when it comes to area modeling, because of NWN's tileset-based design). Since my modding time has always been extremely limited (and practically non-existent nowadays), developing in NWN2 didn't seem to me to be a practical choice given my circumstances.
4) Running NWN2 demanded computing and graphics resources that were significantly ahead of its time. Until recent years, these resources weren't standard on most systems, which restricted the player based still further.
Now speaking personally, with the exception of a few features, I think that NWN2's design is superior, and preferable, to NWN's. Leaving aside CC considerations, if I were starting from scratch today and actually had the time to spend modding, I would likely build in NWN2.
If I had unlimited resources and the ability to spend as much time modding as I wanted I would be all over it. But I don't, and in terms of the amount of time I need to invest in a toolset to accomplish a specific goal, Aurora crushes Electron. Everything is just faster in Aurora...
Third... In two words...
Rideable mounts.
This was a big point for me as well. One of the main things that I wanted for my project (which I did get to do, but which I unfortunately never got to fully exploit) were ridable pegasi.
NWN2 has rideable mounts.
That's good to hear. When did that become possible? It certainly wasn't the case when I needed it.