I respect MMA but only tune in once in a while. Boxing is my favorite sport. So I'll respectfully list all my reasons in loose order of importance:
-The Aesthetics. To me, there's nothing more beautiful than boxing at its best. The fluidity in combination punching, the precision of a clean punch, the subtle timing of a defensive slip, the competence in proper footwork & ring generalship, all of that is beautiful to watch. Not every fight is very exciting, but there's always something to be appreciated in the movements of the fighters. Feints, side-steps, counters, sneaky leads, satisfying body punches, all of those require technical ability that borders on an artform. In MMA, I feel like there is much less rhythm to the fight due to the distance at which they fight, the long pauses on the ground or in a clinch, and the exhaustive nature of the rounds. And there's far less precision in the striking. There are exceptions of course, but there is often so much sloppy offense and defense that it doesn't feel like I'm watching anything special. Fights with lots of twists and turns can be exciting, but I've yet to see an MMA match that could top 100 of my favorite boxing matches. Half the time the takedown defense neutralizes both fighters' wrestling and a lot of MMA matches simply become bad boxing matches with a few kicks thrown in. At that point I ask myself why I don't just watch boxing instead. And on the flip side, when it's heavy on wrestling/grappling, I don't find it nearly as entertaining despite having respect for it.
-The Mastery. MMA fighters are becoming more and more well-rounded, which was the inevitable outcome. That's not to say there aren't experts in their respective fields competing, particularly wrestling and jujitsu, or that it's an inherently bad thing. But because there are so many styles and variables, I feel like there is a lot more randomness involved in the outcome of a fight. There's no guarantee that the winner of a fight excels in any particular area of combat, or that they might not lose a rematch lopsidedly. Additionally, with the talent pool being far inferior to that of boxing worldwide, it's hard for me to believe anyone who is champion at any given time is especially good, or just good right now. This is compounded by the fact that so many top fighters find it hard to stay at the top. In boxing, the cream rises to the top. There's a deep hierarchy you have to climb, and once you're there, winning and losing against people that have made the same climb matters a whole lot. MMA seems like an endless round robin where anyone can lose or win. That defeats the competitive nature of sport.
-The History. Boxing is an ancient tradition and is ever present in our modern culture due to its prominence in the 20th century. There are countless rivalries, upsets, wars, historic reigns, and moments of social significance coinciding with boxing personalities and events. There are various disciplines within MMA that have their own storied pasts, but MMA itself as a sport just doesn't have that rich history. And given the previous point about the difficulty in establishing a legacy, it's proving difficult to forge. It seems like there's a new potential GOAT every year.
-The Personalities. This may come down to me not having enough exposure of MMA, but every time I see an interview or mini documentary of an MMA fighter, it's boring and predictable. I feel like boxers are more a part of their communities and are more distinct individuals for some reason. There are so many mythical aspects to boxers and their gym cultures, and a lot of unique personalities. Duran punched out a horse, Chavez's family lived in an abandoned box-car, Joe Louis was a forgotten war hero, Archie Moore stood on a truck and slipped tree branches, Hopkins came out of a Philly jail inspired by the warden's words, Frazier's training routine in Philly was used for Rocky, Roy Jones raised fighting game cocks, Pacquiao came from nothing to lift up a whole nation, Nacho Beristain's Romanza gym in Mexico City is a factory of champions, Marquez drank his own piss, De La Hoya and Mosley grew up in the amateurs together in Southern California, the Kronk gym is legendary, James Toney loves Burger King, Mike Tyson was a lost soul avenging his pigeon friend turned superstar, Ali was Ali. What UFC personalities could compare to characters like that?
Even today you have guys like Keith Thurman, who is into comparative religion and plays Native American flute, Canelo the ginger sensation who turned pro in his teens and comes from a fighting family, Danny Garcia and his crazy father, Kovalev and Golovkin coming from extremely humble beginnings, Broner the showman, Tyson Fury's gypsy eccentricity. These guys are characters.
-The treatment of the fighters. As corrupt and shady as boxing is, the Dana White and the UFC treats their fighters terribly. They pay is so much lower and they have very few rights as workers. There's much less of a legal scheme to protect fighters in the UFC and the monopoly set-up, while pleasing to fans, is exploitative in many ways.
-Pageantry and Culture. Boxing has a kind of glamour that the UFC and other MMA outfits don't have. There's a classy feel to the fights. The announcers and even the security are dressed in suits, celebrities come well dressed to see it ringside, the commentators are well schooled and articulate, and the promotion usually has a degree of artistic quality to it. Meanwhile the UFC uses a cage, an over the top announcer style, over the top commentators, and styles everything as animalistic and hypermasculine. Bellator and Pride aren't much different. The product overall seems cheapened and the fans seem more like bloodthirsty muscleheads (even if that's not the case).
So, yeah. I prefer boxing.