| TL;DR: because ExtJS sucks. Long answer: 1. The learning curve is really steep. I mean, really really steep. There's a critical shortage of (good) books, video, and tutorials on the web. I guess ExtJS' learning resources should be 0.1% of jQuery's. The examples on Sencha site were still using the 3 version last time I checked; 2. If you need to customize ExtJS, or need something slightly more sophisticated than CRUD screen, then you are pretty much on your own. You'll spend a large amount of time trying to "fight" the framework and your chances you succeeding are very low; 3. It's expensive and its open source license has restrictions; 4. Sencha seems to hide and obscure the access to the learning resources so that you are pushed towards their paid support. 5. It's slow; 6. The error messages (when they show up!) are cryptic. 7. ExtJS was re-designed for version 4, but some things like the Model objects are cumbersome and suffer many usage limitations; 8. It will never be adopted as a general purpose solution on Internet facing webapps for the reasons exposed above; |