The purpose of any avant garde movement is to change the way of seeing or participating in an act so that any preexisting barriers between the act and the participates/observers are broken down.
More simply, to remove barriers that keep observers from being included in the act itself.
Stay with me on this...
People started riding waves doing what we now call body surfing.
Stand up surfing, generally on longer boards, created a barrier of space because you were no longer "in the wave". In many ways surfers were just observers. Not that observing a wave is bad in some way. I spend more time "mind surfing" waves than really surfing them.
After decades of riding long boards there was a revolution of materials and thinking that led to the modern short board and the surfing associated with it.
Although the short board revolution aimed for total involvement, in the end it fell short and todays hottest surfing maneuvers uses the wave merely as a ramp. (Amusingly enough this is called "getting air", something mat riders already have)
Obviously all surfing has merit regardless of device but I think surfing on a mat strives to remove the boundary between what was wave and surfer/rider/observer and allows a more direct connection to the wave.
While we are talking about waves this may be a good time to point out that the waves we ride are only to a small degree moving water. Waves are really energy in wave form that storm winds transferred to the water. We ride them at their terminal end when they break on the shore but the same waves can be ridden out to sea as unbroken swells.
Something to think about the next time you ride an energy wave with your under-inflated air cushion.
Feel the energy, be the wave, you are the avant garde!