As human beings, we rely on comparing and contrasting the things we observe to establish patterns that allow us to navigate the world better and/or shape it how we want.
Asking that question is like asking why we should compare dogs and dolphins as mammals.
Black issues and LGBT issues are social movements.
Specifically, they are social movements that challenged the social hierarchy in the US. We could compare LGBT issues to the movement for US independence, but the second civil rights movement has the distinction of being the largest and most transformative event of this nature in recent memory.
It's a standard. African intellectuals compared their struggle for independence from colonial powers to it; South Africans compared their apartheid struggle to it; Palestinians compare their struggle for recognition to it. Wherever you go, you will find oppressed minorities (which goes beyond race btw: speaking the wrong language can be bad for your safety; just ask the Kurds) draw from the American CRM and its tactics and personalities.
And now, you guys are mad for having set a standard?