Thats because on the side of the moon that's facing the Earth, gravity is more powerful on this side, thus, the moon's gravity pulls the ocean's water in this direction, which is called a bulge. On the other side of the moon, inertia is the one that's powerful, this also creates a bulge. These two forces creating bulges at the same time is what causes multiple high tides.
Hope this helps!
-Daisuke
