Why should it have been Israel’s job to stop a civil war that’s happening in a non-Israeli controlled territory?

But that's the point: It happened in Israeli-controlled territory. They did nothing for a decade after 1993 while de facto still occupying the areas with no change in sight, then wondered why the National Authority lost support in the population and then still couldn't bring themselved to support that peaceful government cooperating with them over radicals bent on destroying Israel.

That's the level of priority peace actually had for Israel. They created Hamas support in the first place by a decade of governing the status quo when the plan should have been to gradually work for more autonomy for Palestinians and peaceful co-existence, then they indirectly supported Hamas by using them for even more excuses to not move on with the planned peace process and now they pretend they have no other choice but killing Palestinians to root out Hamas. When in reality they had a lot of choices for 30 years. And chose the route of escalation every single time.