What exactly prevents Ashkenazim from accepting Mesorah from other communities on things that we have not done in our own community?
For example, what is it about the Mesorah of the Yemenites on locusts, as in the above linked thread, that precludes us from just accepting it? Just because we haven't seen it? Clearly this shows their Mesorah is stronger than ours (argumentative tone intended for effect, not actually to be argumentative)!
Taking an extreme reverse example, can Yemenites marry into Ashkenazi families, trusting the Mesorah that the Ashkenazim are in fact Jewish?
Ultimately, are we just insecure? Is it that we have some (perceived) majority status? Is there something else - a fundamental principle - that I'm failing to see?
Other similar examples:
"Regarding birds, it is clear from the Shach and Aruch Hashulchan that one can rely on the Mesora from another community. But does the same halacha apply to chagavim? There was no uniform answer on this. Many of the Ashkenazi participants asked their own poskim and received divergent answers. While many rabbis ruled against eating, some of the leading poskim in Yerushalaim gave the green light to rely on the Yemenite tradition and eat chagavim." // (Thanks, Isaac Moses.)