Because he's so convinces of himself and thinks he was right all those years that she always comes back to him and choses him over all the others. Everyone is the for now guy but him
Then he's not paying any attention to what's happening outside his litlle I'm the greatest ego bubble. Next week is another good example for that. Both girls are sad or angry and he wants to celebrate. He's totally oblivious to what's going on between "his" girls - but he knows Lorelai so well He's absolultely NO idea who she is, who she became because he is still stuck in 1983 where he was her hero with the piece of pizza.