Why is it considered unsportsmanlike to completely blowout the opposing team?

USA got a lot of criticism for beating Thailand 13 to 0 during the 2019 FIFA Women’s World Cup.  In 2009, the coach for Covenant School in Dallas TX got fired after the girl’s basketball team beat Dallas Academy 100 to 0.  

My own state has mercy rules for high school sports in the smaller classes to prevent blowouts.  If a team is up by 35 or more at halftime then they just run the clock continuously for the rest of the game.  So, if a team’s giving another team a complete butt-kicking, what exactly are they supposed to do for the rest of the game?  I asked my husband about this.  His opinion is that the winning team should just give all of its benchwarmers playtime at that point, which doesn’t always work.  In the 2019 high school football season in South Dakota, Pierre beat Spearfish 103 to 0, and Pierre was down to playing its fourth string in the last quarter.  People wanted the state government to step in and impose mercy rules on the larger classes in high school sports after that game.