Various members have said they don't understand this stuff. Outside of the money there's a huge reason.
Professional boxing has fallen incredibly far over the last 25 years. For decades you could ask people on the street who the world heavyweight champion is and they knew. Now nobody knows which is partially due to the alphabet soup of titles along with many other factors. The only professional boxer competing today that most regular people know is Tyson Fury, and I bet if you asked 10 people on the street only 4 would know him.
Fights like Paul vs. Diaz are trying to do something different with boxing. I won't say it's better than traditional boxing, but it's better than what their professional leagues are doing (cans, alphabet soup of titles, manger's guys only fight his other guys, etc.).
At the end the market dictates how much something is worth. Paul vs. Diaz did $3.2MM in ticket sales, the second largest combat sports event at the American Airlines Center behind a UFC show. So maybe this is what people want to see instead of the same boring, traditional stuff professional boxing has done for decades. Anything - person, business, sport, whatever - that doesn't evolve with the times will die off.