Crushed pineapple comes with the juice but chopped pineapple doesn’t provide that.
Overmixing the batter until it's too fluffy can introduce air and make the cake dry.
Oil helps in retaining the moisture while baking.
Buttermilk reacts with soda to make the cake fluffy and moist.
After baking, cover the cake to trap the vapors within and make the cake moist.