Because Hollywood pays for American heroes. If they made a film of Flight 421 they would have to get an American in there somewhere.
The pilots and flight attendants were awarded the Master’s Medal of the Guild of Air Pilots and Air Navigators in recognition of their “heroic and unique aviation achievement” despite being 7 years after 421. The rescue was more film worthy too, a bunch of villagers is not as dramatic as the Hudson ferry.
421 was never going to sink but the pilots actions saved a lot of lives and injuries just the same as 1549.