Because until the end of the year, Baltimore did not have the established best record in football.
Mahomes was the front runner until they lost a few games in Nov, then Jalen was the front runner almost solely due to 10-1 until week 14ish, then Dak took over for a week until the Miami-Buffalo games, then Lamar took it.
Lamar’s candidacy was heavily impacted by Philadelphia sinking late, and Baltimore beating the only other 13 win team, SF, on Christmas. Which, not coincidentally, was when his campaign pretty much wrapped it up.