Ever the rationalist, SH.

You're right, of course, if standby privileges are just one more item of flexibility that factors into the cost of a ticket. However, there has been no effort to educate the public about this, just weasel words and gate agents who look down their noses at you for being presumptuous enough to ask for a standby. EVen the gate agents don;t seem to know why the rule is there, only that they are supposed to enforce it.
But it still comes down to nickel and diming. The net gain in revenue surely cannot be that great. Who is going to pay perhaps several hundred dollars to potentially save a couple of hours? If AC is emphasising customer service and asking their agents to smile more, it would be nice if the agents were smiling because they were able to help. A smiling refusal could be interpreted as a sneer.