#3 Travel
Mixed martial artists have a specific gym that they train at day in and day out, with some internal changes every few weeks and months. Sounds like a nice routine, right? That's because it is. However when it comes to WWE fighters, they're only ever really home for half of the week if that before they have to jet off on the latest tour around the world.
The miles that they put on their bodies is absolutely brutal with many wrestlers saying that the travel is what cut their career short due to the added stress that it provides. MMA fighters wouldn't be used to that kind of thing at all and they'd likely wear themselves out within a few weeks.
Once again, case and point - Brock Lesnar and to a certain extent CM Punk. As Madonna once said - let's get physical.