Shoot from the hip much? US Soccer isn't limiting anyone to anything.
DA doesn't prohibit participation in other sports. They do prohibit participation on other soccer teams or competitions without prior approval. Some clubs will have further restrictions like prohibiting outside training without approval. But nothing in writing says a 10 or 11 year old DA player is "limited to one sport".
That said, being a part of a DA team is demanding, so taking part in other sports will be difficult to pull off. If the rigors of DA are too much for a kid, with or without other sports and activities, then don't play for a DA team. Nothing stupid about a 10 or 11 year old wanting to dedicate themselves to a single sport or the year-round demands of DA, but it is certainly not for everyone. US Soccer isn't forcing anything on anyone here, only providing an elite pathway as a choice.