I would assume it has to do with the plethora of issues in how the camera isn’t accessible through the official APIs.
Still, yeah, this has me essentially looking into getting rid of my Fairphone and buying another one, more or less exactly what this phone should not be about. But I need ARcore on at least one phone I own - and I have no use for owning two phones.
I guess the people in this forum, who are only users of Fairphone, will never be able to answer those questions.
Maybe unless they #contactsupport, get an answer and care to share the response here.