I'm a new Joomulus user, but I've read something about that in the
release notes of version 2.0:
In this new version we’ve done away with a lot of the parameters from the earlier versions; No more tags generated from content for one
These are the reasons:
The main reason for this was to stop a major bug with PHP expending bytes allocated, which would stop the whole page from loading and leaving the viewer with a lovely PHP error.
The second reason to remove them, and people may not be aware of this, is the search link that all of the generated tags were associated with.