That might be true for Guterres but not for the GA. The delegations that voted were not directed by the UN but by their respective countries. No one forced them to vote for this.
Israel itself gets its legitimacy from the UN resolution in 1949.
> But why would anyone ask them to cease fire against an enemy that won't return the favour?
My understanding of the term "ceasefire" is that it always applies to both sides - so of course during such a ceasefire Hamas would have to stop the rocket attacks as well.