IT organizations often end up putting policies in place that make it easier for them to manage change in the short term but make it harder to allow change in the long term. Add onto that problem the fact that they are responsible for keeping the lights on for dozens to hundreds of different applications, none of which they have direct control over the design and implementation, upgrading to a new version can eat up quite a bit of time and effort.
We just upgraded to WAS 6 a year ago, just as it was about to get EOL'ed. The upgrade and migration involved hundreds of applications and it took over a year to coordinate the change with all the affected teams. I wouldn't be surprised if some shops are still running on WAS 5 or even WAS 4. Not trying to make excuses for IT because they really should figure out a way to provide a smooth upgrade path for their orgs. But the reality in the real world shows that many IT orgs just simply fall short of that ideal and a lot of people pay dearly for it. Luckily for us, IT figured out that they can have separate environments for WAS 5, 6, and 7. It just costs a bit more and IT doesn't have it as easy when they only had to support one version.