Show all the fights? I get the whole network televised prelims. But why don't the shift everything so they broadcast from the first fight on cable then the rest on PPV? Why are there untelevised fights at all? 
Probably some network deal that makes this so, but I reckon it has to do with enticing people to buy the Ppv. Just like companies like spotify offer free trials so you can see how great the product is and want the full experience. 