Because its quite a distance away and there are many countries in-between that won't take that kindly.
Which is why i said, what's the goal here destroy Lebanon or Syria out of spite?
Hezbollah is complete entrenched in Lebanese society and we already that a ground invasion isn't as easy, outside of having a lot of people killed and destroying Lebanese civilian infrastructure what was actually back during the last time Israel and Hezbollah had a ground war?
Lebanon is already reeling from having to accept millions of refugees from Syria, along with the refugees from previous spats between Arabs and Israelis, a war there would be a humanitarian crisis and outright end Lebanon as a country.
Syria is already a mess and Israel constantly strikes against them, so what exactly would be achieved there that Turkey, the US, Russia and other actors have not made? This isn't Gaza where the mess is very contained to a tiny place.