JFS was a very good file system, and at the time when it was released, it certainly was better than ext3. But there's a lot more to having a successful open source project beyond having the best technology. The fact that ext2 was well understood, and had a mature set of file system utilities, including tools like "debugfs", are one of the things that do make a huge difference towards people accepting the technology.
At this point, though, ext4 has a number of features which JFS lacks, including delayed allocation, fallocate, punch, and TRIM/discard support. These are all features which I'm sure JFS would have developed if it still had a development community, but when IBM decided to defund the project, there were few or no developers who were not IBM'ers, and so the project stalled out.
People who upgrade in place from ext3 to ext4 will see roughly half the performance increase compared to doing a backup, reformat to ext4, and restore operation. But they *do* see a performance increase if they do an upgrade-in-place operation. In fact, even if they don't upgrade the file system image, and use ext4 to mount an ext2 file system image, they will see some performance improvement. So this gives them flexibility, which from a system administrator's point of view, is very, very important!
Finally, I find it interesting that you consider OCFS2 "pretty good" in non-clustered mode. OCFS2 is a fork of the ext3 code base (it even uses fs/jbd and now fs/jbd2) with support added for clustered operation, and with support for extents (which ext4 has as well, of course). It doesn't have delayed allocation. But ext4 will be better than ocfs2 in non-clustered mode, simply because it's been optimized for it. The fact that you seem to think OCFS2 to be "pretty good", while you don't seem to think much about ext4 makes me wondered if you have some pretty strong biases against the ext file system family.
 Ocfs2progs is also a fork of e2fsprogs. Which they did with my blessing, BTW. I'm glad to see that the code that has come out of the ext project have been useful in so many places. Heck, parts of the e2fsprogs (the UUID library, which I relicensed to BSD for Apple's benefit) can be found in Mac OS X! :-)
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