In Exodus Chapter 3 God speaks to Moses from a burning bush. He tells Moses that He has heard the cries of His people who are captive in Egypt. The sounds of their oppression has reached Him and He has decided to give them the land of Canaan (Exodus 3:7-10). Israel's deliverance began with God answering the cries of His people. In return God did not plan to simply deliver them, but give them a bountiful land with the ability to sustain them. The Israelites did not pray for what God was preparing to bless them with, God was preparing to bless them above what they asked or thought (Ephesians 3:20).
After bringing plagues on Egypt and forcing Pharaoh to release Israel God chose to lead Israel to the blessing He had prepared. It would not have been impossible for God to teleport Israel to Canaan and gift wrap the Promised Land, but that is not how God works.
The trek from slavery to the promised land was 240 miles. I've seen it described as an 11 day journey (an ambitious estimate). Even at a slow and steady pace, the journey would have been a few months. For this journey God provided Israel with everything they needed. He gave them food through manna. He gave them direction, leading His people Himself. He gave them protection. God equipped Israel for this journey to a blessing they couldn't imagine; a blessing that came about as His choice to answer their prayers. With everything they needed, and fresh out of slavery Israel reacted to their newly found freedom with complaints and gripes.
God heard Israel's prayers, decided to bless them above what they requested, but that generation did not ever see the blessing because they couldn't be faithful in the journey. Sometimes God hears our prayers and plans to lead us to a blessing. We never know what that is, or what God has in store for us, but we need to make sure we don't forego our blessings by exhibiting a lack of faithfulness.