You can't even compare MMA with boxing because MMA is not a serious sport. MMA has no serious infrastructure to recruit top talented ahtletes, it simply just relies on American wrestlers, Brazilian jiu jitsu guys and an Eastern European grappler here and there starting to crosstrain and compete in MMA. In most of Europe MMA is not viewed as a sport at all, only olympic fighting sports are valued and hardly anyone who's successful in olympic sports would cross to MMA because there's less money (olympic wrestlers and judokas do get paid by their countries in Europe, they're better of than in MMA).
The only people who think MMA will overtake boxing are retards who constantly set up fantasy matches between MMA fighters and athletes from other combat sports, claiming that MMA fighters are somehow superior because they would beat those fighters in "real fighting", that's why this forum is full of Ronda vs men threads.
Most of the world doesn't give a shit about that, people want to see sportsmen (and women) from their countries beat athletes from other countries in legitimate traditional sporting competitions with established rules and some history behind it. That's why European countries invest in wrestling, judo and boxing, but not in MMA.
Another thing is that it's an undisputed fact of history that people prefer watching boxing to grappling because boxing is a more beautiful fighting art. That's the reason why boxing has 100+ years of tradition as a modern sport and MMA is a 20 year old obscurity. If people would like to see "no rules" brawls then MMA would have had 100+ years of tradition, but it doesn't. It's not like MMA is anything revolutionary, it could have been invented any time in history, you simply set the fight to few rules if any. Wrestling and judo exist for a long time but have never captured the attention of the public in the same way as boxing did. Boxing is a noble art and aristocratic sport, it has something that MMA will never have. MMA was cool back in the Pride days and that's where most of realistic MMA fans like me come from, this new UFC generation will drive everyone normal away.