Firstly there's the vengeance aspect. Al Qaeda did 9/11, along with many other terror attacks against the US.

Hurras al-din has also given support to ISIS, who destabilized a good chunk of the middle east. It's a bad look since a lot of Americans died to effect regime change in Iraq. If Iraq ends up turning into a full-blown theocracy, it makes our efforts there seem even more wasteful.

According to the Russians, he was trying to gather supplies to make illegal chemical weapons but definitely take that with a grain of salt.

Supposedly this helps US goals in Syria, but TBH I'm not really sure what the US goals are. I suspect that both our current and previous president would have a hard time articulating goals that are consistent with their actions in Syria