In the beginning, nothing was obvious. New things become obvious every day.
So I guess I’m surprised people didn’t discover “avoid wheat” a lot sooner even if it took until the late 20th century to actually understand the mechanism.
I get that "Celiac disease results from genetic abnormal immune response to gluten."[0] I'm not sure what that means, in detail. Perhaps there's a particular allele of one of the immunoglobulin genes. But whatever it is, perhaps other alleles cause "gluten intolerance" of varying severity.