Steelers need to score points in the 1st quarter against the Packers
They could have also won three additional games by scoring a touchdown and perhaps forced overtime in two games by scoring at least a touchdown in the first quarter. So since 2018, just by scoring once in the first quarter, the Steelers could have had upwards of seven wins, and any of which could have changed payoff seedings or gotten them into the playoffs.
Now, going back to the 2004 season, the same principle still holds. A field goal could have won 4 games and forced overtime in 10 more games, and a touchdown minus the extra point or two field goals could have netted 16 additional wins and forced overtime in five additional games.
A touchdown with the extra point would have earned 21 more victories and forced overtime in nine other games. In total, just by scoring in the first quarter, the Steelers potentially could have netted 30 victories since 2004. These additional victories could have had huge impacts on many of those seasons in making the playoffs knocking another team out of the playoffs or the playoff seeds.
Point differential in playoffs
If we expand to the playoffs going back to 2004 twice, the Steelers could have gone deeper into the playoffs with one score in the first quarter. In 2018 a touchdown in the first quarter would have defeated Jacksonville, and in 2011 a touchdown in the first quarter would have netted the Steelers a 7th Lombardi trophy, so yes, by not scoring in the first quarter, they cost themselves at least one NFL title over that stretch.