Has Hamas ratified the Rome convention?
Does the State of Palestine control Gaza?
So here's the actual sequence of events. Israel has occupied these territories from Egypt and Jordan in 1967. Following the peace agreement with Egypt and later Jordan Israel has agreed to work towards giving the Palestinians autonomy in those regions. That culminated in the Oslo peace process where Israel allowed Palestinian leadership from abroad to return to these territories, the PA was established, the territory was divided into different zones (A, B and C) with different responsibility for security, civil management, etc.
Up to this point there was no general recognition of the the State of Palestine by anyone and the consensus was that the future status of the territory was to be determined by negotiation.
The Palestinians (Hamas) decided that the correct response to the peace process was suicide bombers killing hundreds of Israeli civilians, wounding thousands, blowing up restaurants, busses, malls on a daily basis. This was at a time where the majority of the Israeli public supported a two state solution and Israel was negotiating at good faith.
As a result of that Israel elected a right wing government and public opinion went towards the idea that having a Hamas country side by side with Israel was an existential threat and should never be allowed to happen.
The Palestinian authority, having been weakened by Israel, and with Israel's refusal to continue the process, has opted to, with the support of patrons in the Arab world and broader (like Russia), to pursue a path of diplomatic warfare alongside the physical warfare they kept engaging in. They would work through the various institutions like the UN and the ICC to force Israel to yield. With broad support of mostly the non-democratic/non-free world they have been able to increasingly make progress in this area.
Fast forward to today.
This is all political warfare. Just because money and pressure causes country X to say there is a non-existent state doesn't bring said state into existence. The Palestinians can't have a state without a negotiated solution with Israel. They have no territory they control and they won't have unless they can reach an agreement with Israel. The only state they've had was Hamas-land in Gaza and Israel is not going to allow that again. If you need some motivation to understand this please again consider why didn't the world establish a Palestinian state prior to 1967 in the area said world thinks this Palestinian State exists when that land was not under Israel's control. Then this state would have really existed. But the world doesn't care about Palestinians or a Palestinian State. And neither do the Palestinians, they don't want a two state solution either. For them all of this is part of the effort to erase Jewish presence from the middle east. They say it themselves. (not everyone, but most).
EDIT: We should also consider Israel's withdrawal from Gaza as a major event on this timeline.
Either way, there is zero precedence for the ICC claiming jurisdiction over a state that is "created" out of thin air in an area that's actively controlled by another country. This should obviously be unacceptable. The only variable here is that this is Israel. We don't see Tibet or Kurdistan or the Indian state of the Sikhs or Balochistan or Chechnia being recognized with the ICC asserting authority there, that's because either they don't have strong enough patrons or the countries involved have more influence. So there's nothing legal or moral going on here. There are plenty of people on this planet who think they should have their only country but they are not at the intersection of world superpower and cultural conflicts like Israel is.