“So what I don’t understand is why does Lebanon not complain when their civilians also get killed?”
There is still a significant enough Maronite Christian population (30%) who are mostly pro-Israel (think of the civil war which the PLO precipitated (1975-90). Unfortunately from Syria’s screwing up and undermining the Lebanese elections to the Jihading of the Hez psychos and the implicit support of the Islamic population the Lebanese Christian pop have become the de facto dhimmi population there.
If the Leb army has any christians now would be the time to strike against Hez and het rid of them once and for all.