Genetics + humidity + airflow
I encountered the same problem, after just finishing my first grow. I have a carbon filter set up but wasnt running it enough, allowing RH to go up to 80-90% for short periods. After the first two plants that were fluffy like yours, I kept the filter going so that RH stayed at 65% max, 50-60% average, added more fans, and kept temps lower (75ish instead of 80s) and the result was much, much tighter buds. This was the same strain, same breeder, same batch, just different RH.
Try lowering RH/stabilizing it, getting 32watts/ft^2, and better airflow.