Hypothesis 1: In the US, we’re a minority. Plus we may be more and just grateful to be in Jewish company regardless of who what where.
For the most part, both Sepharadic and Ashkenazic Jewry passes as “Caucasian.” Why blow our cover with details of origin?
Furthermore, the US is broad. If one doesn’t enjoy going to shul with so-and-so, for whatever reason, then depending on the location one may be able to resolve conflicts by opting out, by exploring one’s options.
Said options include but are not limited to, finding another shul, davening at a different time, going anyway and avoiding unnecessary contact, and coping by strengthening relationships with others in the community.
In America, the world is an oyster.
In Israel, there is less geographic and interpersonal distance between Jews.
There is competition for resources in Israel.
In America, this Jewish business-person may have to compete with nonJews and whomever else. Even if it is a Jewish business catering to Jews, having competition may add a buffer to the business as there is enough of a demand for companies to coincide and perhaps support each other.
In Israel, someone who is Jewish can be working for a Jew, working with a Jew, feeling threatened by another more productive Jew, feeling insecure about the practices of another Jew in the workplace or shul or shoochnah.
In Israel there is a culture clash. Absorption adds competition. Or the fear of competition. Xenophobia even though we are all Jewish.
Researched:
In the mid twentieth-century, a wave of wealthy Kurdish Jews flooded the borders. Men who were outstanding businessmen suddenly were faced with the only viable options thanks to culture and language barriers, hard labor, construction. It was depressing for many prestigious men to take such a status hit. Ashkenazim and the earlier settlers looked at their fine cloths with ridicule. Their wives had an easier time assimilating.
Anyway… point is that resentment festered. Intergenerationally. This happens. Unfortunately.
When Israelis Moshe and Ovadia don’t get along with each other, then maybe their children feel the rift. It may only be implicit. They may only just prefer to hang out with Ashkenazim or Sepharadim accordingly, reinforced by limited positive exposure to the other.
Instead of having space to step back and get over or cope with differences, close proximity may escalate tensions.
In order to feel safe and secure, Ashkenazim and Sepharadim created mental barriers to confirm their group’s rightful belonging and affirm their group’s beliefs.
Also… both lived under oppression:
Ashkenazim most recently under prodominently Christian rulers and nobility.
Sepharadim (including Mizrachim, which are separate but often lumped into the Sepharadim group), lived under Islamic control and rulers.
They had to battle in unique ways to earn the privilege to live Jewishly.
Whether it was being close to the nobility like Court Jews, and relying on that political connection under Christian nobles, or by being invaluable merchants and confidents to Islamic rulers (so much so that even Muslims with pull looked the other way when seeing such a wealthy Jew riding a donkey), each group earned its place by working up in context with its culture.
Now comes Israel where being Jewish is no longer the most identifying factor. Maybe the OP is referring to the friction. Adaptations to the forces of nature. Human. And more than human at play. Tectonic plates.