All Seagal has done is find one technique that was being under utilized in MMA, the fronk kick. The reason it was successful is because since it's under utilized it's not usually trained to defend. The same thing is happening with the jab, it's just not as noticeable because it doesn't usually knock people out. The jab, a very effective tool, was greatly lacking in MMA until recently. It's finally starting to be more utilized because people are becoming more successful with it. Rubber guard, the truck, the twister, etc... are all examples of this too, they are techniques and positions that the majority aren't training so since they are under utilized they have a higher chance of being successful until everyone gets savy. Then you have to find new ways of going about things little changes evolving the game adding new tools to your box. Thats all the front kick is just an under utilized tool, common in many traditional martial arts.