Johnny come lately finally endorses someone--too late for anyone

So John Edwards endorsed Barack Obama.  Big deal.  He should have 
endorsed someone before Penn.  At this point, what does his endorsement 
mean?  If I was Obama, I would be thinking "thanks for almost nothing". 
  If Edwards had gotten off the pot and endorsed Obama a couple of weeks 
ago, he would have won Indiana and probably would have beaten Clinton by 
20 points or more in NC.  If Edwards' endorsement came before Penn, he 
would have been at least a little closer than 10 points.  Why does 
Edwards endorse him now that the last blue-collar, all-white state's 
contest is over?