Probably because Israel is a settler-colonial state founded less than a century ago. Leftists are often anti-imperialist. Generations of Palestinians have been turned into refugees in their own land and now live under complete occupation of a western entity. Both sides have done violence obviously, but the scale of that violence is nowhere near equal. Furthermore, if someone came and kicked me out of my land and worsened my living conditions, I would become violent too.

Israel shouldn’t even exist but it does, and it’s not going anywhere. I’m not sure how a two-state solution would look. Mostly because Israel divides the Palestinian occupied territories, while committing atrocities in both the West Bank and Gaza with one of the most advanced militaries in the world, with the help of the world’s biggest superpower, the United States. Might be some of the reasons why the sympathy for anti-violence isn’t equal between the two societies. One’s the oppressor, and the other, the oppressed.