Haha, thats a really big pack of assumptions, fiction and emotions. Obviously, when this thread is on NWN2 forums. If you want real answers you need to ask on NWN1 forums.
I can answer for myself - in 2004/5 I and my team was recreating a PW module and we decided we will move to NWN2 once it going to release, one of our builder was invited into betatest. But the promising features turned out to be a wrong. We wasnt able to port our existing content to NWN2 so we had to start over, building exteriors took days where previously it took just hours and the HW requirements were absurd in that time so in the end our team fell apart and thats was the end of store. Please note I do not blame NWN2 for that its not emotional issue.
I was monitoring the NWN2 development in czech republic beyond that, two other teams (and thats only I am aware of) that made a PW for NWN1 and tried to make a sequel for NWN2 had a same fate. From these three independant groups only two builders "survived" and returned to NWN and I am one of them. The other is now working on their old NWN1 PW which is still active. Only one PW emerged for NWN2 in czech republic (compared to over 10 different PWs for NWN1, four still very active today) and that one didnt last very long. I was monitoring the situation there, they had several technical issues with NWN2 engine. Lags, lags, even bigger lags and crashes. In one point they found out that players moving in PW using keyboard keys (WASD) are causing the lags. They had also some HW issues with server - crashing, not properly restarting etc. and after one year this PW was down for good. The current ammount of existing PWs and players playing them shows that the NWN1 is still preffered by both builders and players and the SP scene is definitely richer for NWN1 as well.
As for my own experiences with NWN2.
The camera and control is horrible. Graphic isn't any better, it looks more cartoonish if anything. Loading new areas is slower than in NWN1 (might be due to my not superior HW - dual core 3.0ghz, 4gb ram, GT640graphic - but even if it is due to my HW its not a very good excuse given how bad the graphic is and I can play newer games just fine (AC1,2, Gothic3,PoE,Battlefield 3)). Toolset is a complete mess, I wasnt able to figure out how to work in it, after some time I found out how to paint some tiles etc. but I was really annoyed by it. All this, I could probably somehow ignore, the NWN2 has some good features and ideas such as easier visual effect creating, GUI modifying and... hmm thats probably all. Anyway, NWN1 still leads in engine modifications and extra features using NWNX - I am NWNX developer myself so I know that. And mainly, there is no standardization.
Since I spend over five years for fixing any kind of bugs in NWN1 and improving the graphic/assets and making new features I learned that many of these issues (mainly in scripts) are still present in NWN2 as well. So that would mean that if I would switch to NWN2 I would have to deal with those issues again. And there are actually far more issues than ever was in NWN1 judge from the various fixes for anything that are available for download on neverwinter vault. Sadly, every NWN2 builder thinks he knows better so there are multiple versions of the same (like spell fixes) and the NWN2 community is scattered and everyone recommends different package. So actually, anyone new to the NWN2 who would want to make a serious PW would have to learn about all the issues that NWN2 suffer, all the bugs and all the packages that fixes them and install them one by one etc. And I am not willing to do that again. I would advise to unite together and make a community patch like the one I did for NWN1 so new builders doesnt have to repeat the same painful learning process you guys did.
In the end, the question isn't why NWN1 builders haven't switched to NWN2 but why the NWN1 builders haven't switched to any of the newer game with fewer modding possibilities but bigger player base and thus higher chance of satisfaction. And many of them did...