
why we use struts framework instead of springs

It depends upon your application requirements.In some cases spring is better and in some cases struts is better. In struts2, you can get excellent jQuery tag libraries.Spring also have tag library but not as struts.
Some points to prefer Struts2--
It is very flexible and extendible with Plugins like
Convention Plugin
REST Plugin
getter/setter for Parameter
jQuery Plugin
JSOn Plugin.