Any one of a hundred variables? If I had to put money on it, I'd guess it's that modelers are more difficult to tweak on the fly due to having to go menu diving, so when players dial them in at home, they scoop the amp out and make it sound big, which makes it also disappear in a live environment. Basically it's the players dialing in a lack of mids. User error.
There is no magical "hear it better / cut through the mix" quality about tubes. Seriously. What specific thing about tube amps would you say makes them magically louder or more "mix cutting" than a modeler using a great class AB solid state amp that can output equal decibels?