> White House staff were warned last month not to use insider information to place bets on predictions markets.

Misleading title. They were not "told not to place bets", they were warned not to use insider information to trade. They are still free to trade otherwise. As the article explains it is already illegal to use insider information to trade on prediction markets. So this warning is good legal advice for anyone. It is a reasonable one to give to a group of people who have access to insider information, a large incentive to exploit it, and are likely to be examined under a microscope by rivals.