It just too dam risky for the top fighters to kick back and throw leather. Main events in UFC are often a rather lean dish compared with Boxing. Rampage Rashard was exciting but it weren't Sugar Ray V Haglar.
Stop generalizing, clearly it depends on the fighters involved. There have been some extremely entertaining UFC mainevents and some seriously boring boxing mainevents. I don't understand why you need to make statements like this, it makes you look like an insecure boxing fan. Hagler/Leonard is an awful example to use btw
