It's mostly an ecosystem thing. Large companies follow the lead of their vendors and Oracle/IBM/HP all push Java. There is a vast array of third party tools and software packages for doing boring enterprisey stuff like monitoring and integration. If you want to integrate or extend one of the big ERP or CRM systems that is mostly Java. At this point there are lots of people that can be hired with passable Java skills and most consulting outfits have large Java programs. Admittedly this is something of a positive feedback loop that got started because the big vendors stared it 15 years ago.

As for team delivery speed it is certainly possible to deliver quickly. The dynamic languages have definite advantages over Java. There is less XML/property/configuration stuff to manage for instance. But the Java frameworks are actively developed and they get better all of the time too. Delivery speed is mostly a team and organization thing. Large orgs can take forever to deliver the simplest of things. It can take forever for people to decide what they want. You might have to get permission from three different VPs. You may have to schedule a series of meetings to have a decision made and it can take a couple of weeks the find time when all stakeholders have open time on their calendars. You may be dependent upon cooperation and resources from another team that isn't really motivated to help you because they have their own stuff going on. So it's not really a technology problem, it's a management problem.