Alien Nation (1988) - pretty good, but what's the deal with the milk?

Okay, so I just watched Alien Nation (1988). I'm trying to catch up on some of these '80s sci-fi classics I missed and this one was...interesting! The whole premise of aliens integrating into LA society is kinda cool, and I liked James Caan as the cop, even if he was a total jerk at first. Mandy Patinkin as his alien partner was surprisingly great too. The whole 'learning about each other' buddy cop thing worked really well, I thought. But what really got me scratching my head was the milk thing. Like, they're addicted to sour milk? That's the thing they need to survive? It felt kinda random and weird, and I was wondering if I missed something. Is there some deeper meaning to the milk that I just didn't pick up on? Like, a metaphor or something? Also, the whole ending with the sunrise and the alien enslavement plot...it felt a little rushed, didn't it? It was kinda dark but then it just kinda...ended. I'm not sure if I loved it or hated it. Anyone else have thoughts on the ending or, REALLY, the milk thing? Seriously, someone explain the milk to me!