These could have similar issues with gaps in FDIC protections due to money is being “managed” by intermediaries or because of the type of account. Their fine print discloses as much.

As a sibling comment points out, Fidelity is seemingly a reputable enterprise with other business that would be adversely effected by poor management of this product and the reputation harm that would come with it.

Among other features Wealthfront are trying to manage around the $250K FDIC limit for you by moving your money into multiple insured accounts - this is probably a new area with not enough regulation.