What does it matter to you? Did you see the stadium? It was full on both days. It was even full for the stupid celebrity softball game. Obviously the people thought enough of the festivities to fill the stadium and look happy about it. Sports are entertainment, and sports players are entertainers. It's their job. Did they look miserable to be there at the all-star game? Didn't look like it to me. Seemed like they were enjoying themselves and the chance to be recognized as one of the best in their profession. I made a few all-star games in little league and I didn't turn down the invitation just because the game didn't count for anything. Playing baseball is fun. Playing baseball with a team full of really good players is even more fun.
No one forces you to watch the ASG or the Pro Bowl, and the players have a million opportunities to come up with an excuse not to show up if they really don't want to go. Should the game count for home field advantage? Who cares. Before they did it this way home field used to alternate every year between the leagues. It has roughly the same chance of doing so under the current format as well.
"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat