I assume that many of us who were heading to EWR/JFK/LGA on Friday night had our flights diverted to other airports away from NYC and sometimes cancelled at those other airports.

Could someone explain, though: if a flight is diverted to an airport far away from the destination and then cancelled, why does US rebook passengers on regularly-scheduled flights to the destination airport rather than just flying the plane (from the original flight) to the destination airport and taking the passengers along, especially when the original plane is scheduled to do a trip from the destination airport the next morning?

Basically, if people are on a plane that gets diverted, but the plane has to eventually make the trip to the original destination, why doesn't US just let the passengers fly on that plane when it finally makes the trip, especially if the alternative is for people to fly on regularly-scheduled flights late the next day, resulting in lengthier delays?

Thanks.