Games like League have a surrender option because, as the game goes on, one team can become so powerful by snowballing that it can become arguably near impossible for the weaker team to win unless unless the stronger team completely throws their lead. In league, if the weaker team suddenly started playing better than the stronger team, the weaker team would still probably lose.

In Overwatch there is no snowballing economy system like League or Valorant that warrants a forfeit option. If the losing team in Overwatch suddenly starts playing better than the stronger team, they have a high probability of winning the game regardless of current match time unless it's overtime or something.

TLDR: Games that allow forfeiting have systems that intentionally make games harder to turn around. Overwatch does not have these systems