Developing for the web sucks. Things that should be easy are very hard. It is alot like developing embedded applications in a very restricted environment with random, non-sensical limitations, only worse! Worse, because its really like developing for several such ever-changing environments at once.
So, why do it? Why subject yourself to that torture? On the desktop, you have basically limitless capabilities with relative ease. Its not as much of a moving target. The easy things (with the right tools) are damn easy.
Well, when I put on my user hat, I love web applications. I know that opinion isn't universal. A lot of people still prefer desktop applications. But a truly well crafted web-application, is for me, a joy to use. And I love the open web. Its a hyperlinking, cross-platform, mash-up-able free-for-all.
To summarize, I want to build applications that I would want to use.