One idea that has been thrown around in our poly group and in other minority groups I am involved in is that anyone who is already part of a marginalized minority is at higher risk by being "out" about belonging to another marginalized minority.
Therefore-with the higher risk-they may be unable to safely be out.
For example, someone who is LGBT is at risk of discrimination.
But, someone who is LGBT and black is at a higher risk of discrimination-because they risk being discriminated for both being a minority=black and a minority=LGBT.
Someone who is LGBT, black and a woman has even higher as woman=minority, black=minority and LGBT=minority.
An LGBT, black, female, poly.... at that point the risk of losing work, home, personal safety is so high that it is literally mind-boggling the life risk they would be taking.
I tend to think there is probably a lot of truth to that concept. It makes sense to me and I've seen how it works with people who are racially, gender, sexual preference minorities in our community.