Agent use might indicate large disposable income, but agents locking up inventory that other passengers with large disposable incomes could have purchased is a net negative unless the agent-using passengers actually keep the seats.

As plenty of others in this thread have pointed out, agents tend to book first and then cancel later if they don't get post-approval from their user. That ruins the experience for all the other potential passengers who could have purchased those tickets and it's clearly better from a business standpoint to prioritize the other potential passengers over the jackasses who care so little about their seats they couldn't even be bothered to book the seats themselves.