Without completing the missions on 3/6/10, no one on the team gets money. If that's not motivation enough to do an objective, I don't know what is.
I don't think a lot of people are complaining about not getting points for helping on objective waves, but if BW decided to add that in, I wouldn't have any complaints. Like Rhole said, those points are just epeen. You don't actually get more exp or credits for having a higher score.
You're mad that people don't guard you while carrying the objective. I'm actually more pissed off about all the bad carriers in my games. They race me to the objective always pick it up right before I get there with some STUPID class like a Phoenix Adept with 0 points in toughness. Then, instead of giving up the object to our sentinels or krogan vanguards, they walk a retarded path right into the middle of the enemy wave, like, "Hai guys! Ready to get this gang rape started?"