AFK/Leaverbuster

So last night I was playing some league and everything was going fine. I started having internet troubles and was hit with a leaverbuster(normal draft mode, not ranked thank goodness). I completely agree with the leaverbuster but can someone explain to me why the whole client is unusable during the low priority? Like im already being forced to wait 20 minutes for a game but why cant I visit the store or something while Im waitin?