Boxing is in a bit of a vicious cycle and has been for some time. During Ali's prime boxing was more popular generally. It was a mainstream sport that lots of people watched. It was also going through a golden era with regard to talent especially at the heavy weight level. There was Ali, Frazier, Foreman, Liston all fighting at the same time which of course amplified the popularity.
Now boxing doesn't have any of the all time greats boxing and its less popular, meaning its unlikely to have greats start boxing again. Add in how much less acceptable head injuries are in sports, the decline of youth boxing in the USA and the rise of MMA and it is unlikely we will see boxing be anything more than it is now, an occasional big fight for a couple of top contenders and not a lot else that makes it into the general mainstream.
As for moving like that, part of it is that bigger guys more generally move better than they used to so the difference isn't as pronounced but its also Ali being special.
I wonder if the drop in popularity has to do with title bouts moving to pay per view. I've never been interested enough to pay to watch but if it was on network, I probably would have...
Now boxing doesn't have any of the all time greats boxing and its less popular, meaning its unlikely to have greats start boxing again. Add in how much less acceptable head injuries are in sports, the decline of youth boxing in the USA and the rise of MMA and it is unlikely we will see boxing be anything more than it is now, an occasional big fight for a couple of top contenders and not a lot else that makes it into the general mainstream.
As for moving like that, part of it is that bigger guys more generally move better than they used to so the difference isn't as pronounced but its also Ali being special.