I'm wondering if the reason is that there are simply so many match requests that Apple's network is not able to readily meet the demand. One reason I believe this may be the case is that I've never subscribed to iTunes Match, yet when i upgraded to 11, I also observed the "Sending Information To Apple" message for what seemed to me to be a long time. Having never subscribed to iTunes Match, I clicked the "X" to stop the process, and now I'm left with lots of songs that have been assigned the iCloud "Waiting" status, which I can't find a way to change without taking the initial action of subscribing to iTunes Match. So the question I will probably post as a new discussion might be something like, "Is there a way to resume a canceled automatic match process to resolve the "Waiting" iCloud status designation after an iTunes 11 upgrade without subscribing to iTunes Match?"
To summarize, I think it's likely that demand for matching is too great to be handled quickly through available network server resources, and that's at least partly due to the fact that every connected user with an iTunes library is undergoing the match process upon upgrading to iTunes 11, not only those for which an iTunes Match subscription was already active.