JSP web apps can be built quickly as well. Eg. you have the JSTL tag library, and orm frameworks such as MyBatis or Hibernate. And there are also other things for simplifying, decoupling and modularizing a webapp like the Tiles framework, Struts, Spring MVC frameworks etc.
Now, I know for a fact that there are some other advantages php or rails apps have, particularly the lower price of hosting and possibly smaller memory requirements, but I'm wondering if there are any other reasons that JSP/Servlets/Java based small webapps are such a small minority and why adoption seems to be rather low for small to medium web 2.0 apps.