Israel is a US client state and generally does what the US wants it to do so of course they will normally veto critical UN resolutions.
The US did not ban Israel's sourcing Chinese weapons, the US banned Israel from selling weapons to the Chinese. This is not to do with loss of profits directly but because it was against the US national interest to improve China's anti-radar capabilities. And where the US national interest clashed with the Israeli national interest, the US forced Israel to back down. Similarly when Israel was told not to bomb Iran, it also was forced to back down. These things would not happen if Israel directed US foreign policy.
When the IDF kills Palestinians, it does not go against the US national interest and the use of high tech modern weaponry certainly boosts the profits of the defence industry, who have much more influence over US foreign policy.