No, Mera, that is not why they are not pushed to Curse. Using the svn/git/etc uses *more* bandwidth for Curse (part of why wowace started having problems and created the zip packager on the original site), copies on wowace are working copies with untested and unfinished buggy code most often, and authors will tag a version as a beta or release version (sending it to the curse page) for normal users' consumption. Users updating their alpha versions for new locale updates, tiny dry-code fixes, etc, etc every day are precisely why wowace went under and had to team with Curse. It is all detailed in various threads and sticky posts over there.
But all of that is off-topic. Still, though, people need to understand that wowace is not where normal users (non-alpha testers or devs) should be sent for their addons.
Saving a second or two on loading time while the client sorts through library versions at login is not the same as saving on memory/cpu when playing the game. This is an old post about WAU, thus it is not stickied any longer, but it still describes whether someone should use standalone libraries or not:
http://forums.wowace.com/showthread....lone+libraries