Liberation does not happen by itself. Slave drivers do not let their slaves go voluntarily.
Pharaoh also hardens his heart and refuses time and again to let the Israelites go.
Liberation for Israel happens at the same time, and in the same event, as the judgment upon Pharaoh and his army. The judgment over the oppressor is the liberation of the oppressed. The liberation of the people (Exodus 15:2–13) occurred because God’s fury consumed Pharaoh and his army, and he shattered them (Exodus 15:6–7).
6 Say therefore to the people of Israel, ‘I am the LORD, and I will bring you out from under the burdens of the Egyptians, and I will deliver you from slavery to them, and I will redeem you with an outstretched arm and with great acts of judgment.