Turbulence comes from moving through different parcels of air. Aerobatics takes place in a relatively small volume of air (1km x 1km x 2,000ft), so its less likely to involve turbulence from moving through different air parcels. Often a sequence will be done over a single paddock. T28D also reminds that a large amount of the time aerobatics is done at low speed.
A long cruise descent poses the biggest risk from turbulence.