The Seahawks played an anachronistic defense in 2019. Specifically, and to quote Vincent Verhei’s essay on Seattle in the 2020 Football Outsiders Almanac:
“[T]he Seahawks essentially played the 2019 season without the benefit of a nickelback. Seattle used a base defense 69% of the time, nearly twice as often as the next team (Arizona at 38%).”
Passing the ball has never been more important to winning in the NFL, and it was already by far the most important part of winning in the NFL. Offenses have adapted. Fullbacks are rare. Tight ends are increasingly primarily pass catchers with only a token contribution to the run game.