Originally Posted by Dollar
Maybe it's done to give a sense of space. Lighter colored headliner gives the impression of more room where a dark headliner will feel like the top is closer than it is. Just like interior design. Darker colored rooms feel smaller vs. a lighter colored room.
It also brightens the interior up a bit.
I had an Explorer a few weeks back for a rental and it had an all black roof inside. It was strange, it made the whole car feel smaller and gloomier.