Two days after the October 7, 2023 attack that Hamas launched on Israel the UK updated https://www.gov.uk/foreign-travel-advice/israel to "advise against all but essential travel" to all of Israel (and to "advise against all travel" for select portions) (previously most of Israel was "green").
The US Department of State's Travel Advisory for Israel, however, was last updated on October 3, before the October 7 attacks, and places Israel at level 2 of 4 ("Exercise increased caution"). Now, sure, on October 9, https://travel.state.gov/content/travel/en/traveladvisories/ea/situation-in-israel-2023.html was posted, but that's not an actual update to their safety ranking thing.
So it seems to me that the two possibilities are (1) that it just takes a good amount of time (relatively speaking) for the US to update their travel advisories or (2) that the US thinks the recent events in Israel do not change the overall security situation of Israel?