Why we don't have attributes in config like context??

What would you use them for?
Remember, there is only one ServletContext object per web application (or per JVM in a cluster). So it makes sense for a servlet to be able to set attributes on the context object so they may be retrieved by other servlets.

However, there is one ServletConfig object for every servlet. If a servlet were able to set an attribute on the config object... the only servlet that could retrieve it would be the same servlet. There is simply no reason for it.