Why didn’t Pharaoh want to let the Israelites go?

Because this: firstly, it was a manifestation of weakness for the ruler, and secondly, Egypt was losing cheap labor. One way or another, but the Israelis, or rather the Jews, left the Egyptian lands. After that, a forty-year wandering in the desert awaited them, until they reached their homeland – the land of Canaan. In fact, from here they came to Egypt a very, very long time ago.