Probably the main reason this will never happen is the UFC has struggled to get the events sanctioned in the US. When it was banned, it was largely due to the fact that there was no rules and no weight classes, kind of a free for all Bloodsport is how it was looked on as.
So to be a legitimate sport, they came up with rules and weight classes. This is my understanding on the subject.
I wouldn't find it entertaining either, the competition of two skilled fighters with equal (or supposedly near equal) strenght is what I find most appealing about the UFC. This is why when Hughes defends 5 times in a row and so does Chuck, it's a great feat.
If you like free for all fighting, just watch those videos of Kimbo (lol), that's what those are all about.
Just my take on this.