P2p/Grid Computing seem like a promising concepts. JXTA looks like the only all in one framework for it. Is there a reason this field is so sparsely pursued?
I have lead the release of JXTA 2.6 and 2.7 - JXTA is not completely abandoned. Some people have posted patches on the 2.6 branch and it could easily be merged with the 2.7 branch.
There are many reasons why people did not carry on participating to JXTA:
Oracle did not follow-up on their duties regarding project governance, which left the project in a limbo state.
Oracle did not follow-up on a request to move the project to Apache.
The code base was old. We cleaned it and implemented unit tests. But in order to move the project to the next level, it would have required a lot of rewriting. Not enough volunteers.
But more fundamentally, the reason few P2P frameworks took off is because P2P is fundamentally complex when you get into details. Most people don't get it until they start putting their hands in the dirt. It is not possible to implement P2P 'in a simple way'.
So nothing to do with all-Java clients, licensing fees or others.
Update (August 2013): You thought JXTA/JXSE was dead? Well someone worked further on it and developed a DZone tutorial (unfortunately, SO does not allow links to Dzone, so Google: JXSE and Equinox Tutorial).
Update (November 2013): A group of people is working on new releases of JXTA. For more information, register on the mailing lists.