Different, more involved process of isolating it, or supply/demand would be my guess. Maybe KK or someone in the know could tell ya.
Whey is a byproduct from the manufacturing of other foods. It was a waste product that now brings in extra revenue for manufacturers.
dicks! they should give it away at the back of factories for free lol. And i have never bought any casein, it's too expensive.
If I remember proteinfactory.com got their start by hauling waste whey away from local cheese makers. The same story probably fits for other bulk sites like allthewhey.com. Human milk is 65/35 whey to casein while cow milk is 80/20 casein to whey. We get the benefit of picking up whey on the cheap. They're doing us a huge favor.