Hey, good question...
Aerobatics is all about power to weight and for large power you need a large fine pitch prop, and that needs to clear the ground... and for weight fabric is lighter that Aluminium.
Consequently you GENERALLY find that medium level aerobatic aircraft are fabric covered and tail draggers.
Now that being said most of the top performance aircraft are mostly metal or now carbon fibre as this helps with rigidity and increased the G limits, however due to the prop size they remain tail draggers.
Cheers and again good question
Wombat