Why would the US support this? In fact, the US has been pretty vocal about its opposition to these developments. Regardless of this though, you greatly over estimate the influence of American politics on internal affairs in Israel.
Also, nobody gives a shit about what the UK supports lol.
A continued military presence in the area and reason to keep the military industrial complex spun up. Same reason for basically every intervention/conflict/war since the American revolution in the case of the us.
In both cases because they're wildly unpopular and in the case of Afghanistan because it started the war on terrors ability to strike anywhere anytime. Make no mistake the us is still in the area and droning with impunity.