If you make the periods sufficiently short (a few minutes) you then provide opportunities where you will have increased luck and decreased luck. This helps get you hooked on the game. If you have periods where you get a lot more triple spins, you get excited. Then you go through a period where you get nothing, you want to keep playing to get another one of the better luck periods.

It IS theoretically possible for things to be completely by chance, but things run far too much in streaks for that to be statistically likely. And even if you were theoretically in a period where the drop rate had dropped, it doesn't mean it's zero. It just means that the drop rate is lower.