So my question is , why did they decide to use ioquake3 instead of OpenArena engine ?
Heya,
I packaged ioquake3. It's for easier maintenance/security support of Quake-3-engine games, yes; ioquake3 is the "furthest upstream" version, so it's easier if we do everything else relative to that, and try to push all the bugfixes into upstream ioquake3 so derivatives and distributions can stop worrying about them.
The engine part of "openarena" in Debian is actually already a step in that direction: it's a svn snapshot of ioquake3 (corresponding to the version that the OA engine tarball seemed to be based on), with the OA engine changes from the tarball, some bugfixes from ioquake3, and some Debian-specific changes applied as patches. See
http://patch-tracker.debian.org/package/openarena/0.8.5-4 if you're interested in how it breaks down.
I've opened bugs on ioquake3 bugzilla for various of the OA engine changes, so they can hopefully get into ioquake3; for the moment we're applying many of them to Debian's ioquake3 as distro patches. I haven't opened bugs for all of the OA changes yet - I left out OA's bloom renderer feature, for
instance - in an attempt to get at least the bugfixes committed sometime this decade :-/