While all these are technical reasons for migrating Struts 1 to 2, I would say that the business reasons are far more important. If you've an existing web application built with Struts 1 and it is robust and serving the customers well, there is really no business value or sense to just do a technology upgrade or refresh.
My point is to not get carried away by all the technical reasons and forget that all work needs to be justified in dollars and cents.