I agree, it's the world's worst humanitarian crisis and you are totally right, the devaluation of human life threatens us all. Years ago I worked in communications and PR in a non profit and I'm always interested why some crisis get "traction" and some just don't. So apologies in advance if my observations sound a little cold, I have my communications hat on here.
I think it's a little bit of racism - pick up on the Rwandan genocide was poor initially. Africans killing other Africans kind of thinking.
But in 2005 there was large movement for the people of Darfur. So people are out there are ready to support the cause:
Another reason is that it's really difficult for journalists to get access to Sudan. Journalists within Sudan have had to flee. And generally internet and media infrastructure is down in many of Sudan's states. So there is a lack of content basically. Stats are all well and good but what really gets compassion is seeing how the conflict has affected a real person. Compelling content is the single most important factor in getting attention
There is no clear "baddie" and the situation is really complex so it's hard for people to get their head around.
There also are not simple answers (and by simple I mean simple to explain rather than simple to implement)
Also people's attention is really fickle. The situation in Sudan deteriorated over a long time and the eyes of the would quickly move on. It's always the case that the attention of the world is only on one crisis at a time. I can nearly list them going backwards - Gaza now, before that Ukraine, Afghanistan in 21, bit of Myanmar in 19 for a while....I'm sure I am forgetting a few but you get my point.
That's my two pence anyway.