As it was explained to me, it is about duty cycle. The condensation doesn't instantly accumulate enough to make droplets and run all the way down the drain, so

As it was explained to me, it is about duty cycle. The condensation doesn't instantly accumulate enough to make droplets and run all the way down the drain, so if the compressor only runs briefly the condensation is still on the fins and evaporates again. You need to keep the compressor going long enough that you actually have water running down the drain, instead of condensing/evaporating cyclically.