Why I dont see YUI used that much often

I have been using jQuery/Prototype/ExtJs and other frameworks for last two years. These frameworks have been very useful.

I switched to YUI recently and finding the learning curve a bit too steep. Also the framework is not making my life as easy as with Extjs or Jquery.

When I consulted several other developers no one seems to be very enthusiastic about YUI. Very few of them have actually used it. Of course this depends on where I stay and what kind of people I interact with but can I say safely that YUI is not beign received as enthusiastically as jQuery? Why is it so ?