Because it's Israel filling another country with small remote mines, not an "unfriendly" (to the US) country.
This is the nature of the game with these people, they're not an established military so what are you supposed to attack in order to stop your children being blown apart at a soccer game?
https://www.abc.net.au/news/2024-07-28/golan-heights-strike-...
https://www.timesofisrael.com/massive-tragedy-kids-killed-in...
Edit: Added another source because I saw some cowardly accuse me of "spreading Israeli propaganda and then deleting their comment, there's a non-bias news outlets story too, the ABC".
The Magdal Shams is a village in the Golan heights, which is a Syrian area that is illegally occupied by Israel. At the very least, it is a huge leap of faith to assume that the families of the victims condemn Hezbollah or Israel or who they think is responsible.
Whatever your beliefs are, I suggest not jumping to conclusions so quickly, especially on such a complicated topic
Misdirected attacks happen all the time in warfare, and tragically there's nothing in the slightest bit surprising about it. The circumstances around the Majdal Shams attack are still unclear, but it's highly unlikely that Hezbollah would deliberately target a soccer field in the middle of a Druze community in Israel-occupied territory. Most likely it was affected by EW or simply went off course.
So yes, "accidentally blew up a soccer field".