I believe that one of the reason is lack of good web-applications framework for quick development. There is nothing like django or rails, so if you need to have non-trivial application created in minimum time java is not the best platform.
In case when your team consists of plenty different skill level developers java is much safer platform.
Performance of the application and hosting is not a problem.
Hosting of java application usually is much easier than everything else and performance of jvm very good comparing to other platforms.