You're looking at this ecosystem
after we've already gone through multiple versions of EJBs that are all very different from each other, several different JMS implementations from many vendors now deprecating them (IBM is deprecating a couple of their JMS implementations for cloud services in favor of a hosted Kafka offering, for example), and the endless XML-based configuration of all services and their components combined with a lot of tight coupling requiring different services to be re-deployed upon updating their EJB entities or face class unmarshalling problems. I'm not a fan of sloppy configuration, but there is historically far too many things that were necessary to configure to get a basic JEE service started.
A lot of what's in JPA now came after Hibernate became such an industry-wide standard and because EJB 2's EntityBeans were so awkward. For early adopters in the 90s, EJB 1.0 was really, really difficult to work with and overall a frustrating experience compared to using Spring + Hibernate. This pain was much more keenly felt for enterprise software start-ups that couldn't afford release cycles and deployments that take so much time.
JMS is not the end-all be-all of enterprise messaging either and the J2EE ecosystem made certain technology innovations more difficult due to its byzantine nature. The AMQP working group came out of their frustrations with JMS and it includes a lot of experts with JMS implementations from the usual vendors.
I challenge you to find communities of developers other than H1Bs, older, offshored, and other disadvantaged (and in no way technically deficient either!) workers that are writing anything with EJBs for their jobs these days. Look at the career possibilities for these places as an engineer - do you imagine IT outsourcing and banking backends is something highly motivated and talented engineers would find fulfilling when there's other options? Furthermore, I challenge you to find operations teams that enjoy supporting these systems compared to architectures built around microservices / SOA using lightweight containers using, say, Kubernetes. J2EE architecture is simply not easy to maintain in production with typical enterprise sysadmins despite the billions spent on improving them over multiple decades now (and due to the hostile atmosphere of enterprise software vendor-client relationships impeding technical progress since time immemorial), and this is a deal-breaker for large organizations that are trying to reduce operations costs.
Even though ultimately we as an industry seem to be reinventing the wheel constantly probably to keep ourselves busy rather than to build highly maintainable software, this is preferable to millions of developers around the world in a monoculture writing constantly refactored and improved COBOL and Fortran if we approached the world of software with the JEE vision. It's been shown academically that for software reliability and maintainability, if you need to rewrite more than a certain percentage (I believe it was around only 30%) of the software, it is more economical and practical to rewrite it all. It is the rigidity of the JEE vision and competing enterprise standards that made interoperability and thus freedom for motivated, creative developers difficult that pushed them away from both larger companies and toward smaller companies united by open and probably less stable ecosystems. Moreover, it is really difficult to argue that the MIT Approach [1] fits everywhere in the software world and also that there is no merit to Worse is Better.
It's funny that you mention RoR in that there's been some concern by the community that it's becoming more like J2EE. It's a bit sad in a way because if everyone writing mature software winds up ultimately implementing J2EE, it has shown how little progress we've made as a software community despite so many different software design philosophies gaining market traction.
[1] https://en.wikipedia.org/wiki/Worse_is_better#The_MIT_approa...