There is a simple question and also a more complex question. The simple question is why most states are not willing to accept the 'right of conquest' in the case of Israel. The more complex question is why the West Bank is not legally considered now as part of Israel.
I will try to answer part of the complex question, since parts of it cannot be overlooked and I am not sure if everyone knows them, than I will proceed to the simpler question.
So, the legal status now. Legally, Israel itself does not consider the West Bank as part of it, except for East Jerusalem. This is the reason why the Supreme Court struck down the "Hasdara Law". This is the reason the law that imposes that plastic bags be sold for 0.10 NIS did not pass in most of the West Bank. The territories are under the Military Governorate, and are in a state of military occupation. East Jerusalem and the Golan were annexed, albeit with an ambiguous formulation ('Israeli law is applied to...' instead of 'these territories are part of Israel'). However, the Israeli Government tries in many ways to make the territories "feel" as parts of Israel. It gives to its Israeli residents the right to vote for the Knesset (as opposed to Israelis in other countries, who cannot vote), it produces maps where the Green Line is not shown, it tries to apply as much as possible the Israeli Law to the settlements and so on.
For this reason, the Golan Heights (and East Jerusalem) have a completely different status from the West Bank.
I could go on and on about the legal status of the territories, how the Israeli Government is defining the West Bank now as "disputed", rather than "occupied", territories, and so on, but since we are in Politics.SE and not in Law.SE I suppose you are more interested in the reasons that lie behind the political moves, rather than the legal content.
So the reasons why most states do not recognize Israeli claims are (in my view):
First of all, Israel itself uses ambiguous formulations regarding its rights to the territories. Especially for the West Bank, there is a broad consensus that recognizing it as part of Israel bears an obligation to provide citizenship to its (Arab) residents, a really existential threat for the State, so it is not in its interests to consider it as "part of the State". Similarly, many legal terms used by Israel (and by Palestinians) are bogus. For example, outside of Israel, there is no law, treaty, contract between nations whatsoever that uses the term "defensive war". It is not a legal term, and if you think about it it is rather subjective, since Israel was the one that first invaded Egyptian territory and that the eyes of the Kibbutzim were set on the Golan already before the war.
If the "right of conquest" is recognized, this opens an enormous can of worms. If it is accepted that you can conquer a territory and make it yours, expect tensions in the South China Sea, in the vicinity of Russia, in the West Sahara and so on. It could provide an incentive for wars.
Israel is at best a regional power of 9 million inhabitants, very unpopular among its neighbors and in general in the world. Recognizing its claims attracts the antagonism of 300 million Arabs, and billions of opposers. Netanyahu is somewhat successfully fighting that and applying a doctrine that states that strengthening the country economically and militarily will automatically produce diplomatic and popular achievements. Despite his efforts, Israel is still very very unpopular and very much isolated as compared, for example, to Sweden. The incentive for not being friends with Israel is simply bigger than the incentive to be friends with it, at least for the moment.
So, international recognition of the West Bank as part of Israel is almost nonexistent since Israel itself does not recognize it at such, since it would create a dangerous precedent and since Israel's position is diplomatically very weak.
Recognition of East Jerusalem and the Golan is a bit more present (the USA decided to accept the claim of a 'defensive war' for the Golan and moved their embassy to the No-Man's-Zone outside of 1967 lines, some countries recognize 'Jerusalem' as the capital without specifying West, etc), since Israel itself demands it, some allies go with it, and especially the Golan has a lesser potential than the West Bank for evoking the Palestinian problem which alienates the world because it is considered more 'Syrian' than 'Palestinian'