alt Hacker NewsI don't think they're actually trying to stop you. Rather it's a public stance to protect them from customers' misaligned agents. They don't want to be liable for actions your agent took on your behalf; e.g. refunding a ticket when your agent bought the wrong one.
It's about segmentation or price discrimination. I was able to get the same hotel room $50/night cheaper when my agent browsed from a different country for example.