CBF's view of cooperation isn't based on a theological or doctrinal position. It's more of a realistic recognition that cooperation takes place in areas where there's consensus and agreement, and controversy is avoided when they don't get involved in areas where they don't agree. CBF leadership likes to appear tolerant and accepting of diverse perspectives, and to take a perspective that would look exclusive to those within their ranks who don't accept the view that there's nothing wrong with homosexuality doesn't fit with the image of tolerance and acceptance they want to foster. They want to be the Baptist group within which people who hold differing perspectives on hot button theological issues can cooperate and work without conflict.
On the other hand, Chris, there might be some real hope for quick change. A whole lot of conservative Evangelicals seem to have come around to dropping their opposition to sexual assault of women, pornography, adultery and divorce in just one presidential election cycle. So it might not take much for CBF to come around.