Why is there no manna today?

In Exodus we learn that the Lord called Israel into the desert and then provided food for them supernaturally:

Ex. 16:11 And the LORD spoke to Moses, saying, 
Ex. 16:12 “I have heard the grumblings of the sons of Israel; speak to them, saying, ‘At twilight you shall eat meat, and in the morning you shall be filled with bread; and you shall know that I am the LORD your God.’”
Ex. 16:13  So it came about at evening that the quails came up and covered the camp, and in the morning there was a layer of dew around the camp. 
Ex. 16:14 When the layer of dew evaporated, behold, on the surface of the wilderness there was a fine flake-like thing, fine as the frost on the ground. 
Ex. 16:15 When the sons of Israel saw it, they said to one another, “What is it?” For they did not know what it was. And Moses said to them, “It is the bread which the LORD has given you to eat. 

For the Israelites in the desert, the Lord supplied a special bread sent down from Heaven. This was a unique, one-time provision intended to do far more than merely feeding a group of people. God's plan was intended to picture the coming of His Son, the Lord Jesus Christ.

The Lord Himself said He is the bread from Heaven:

John 6:31 “Our fathers ate the manna in the wilderness; as it is written, ‘HE GAVE THEM BREAD OUT OF HEAVEN TO EAT.’” 
John 6:32 Jesus then said to them, “Truly, truly, I say to you, it is not Moses who has given you the bread out of heaven, but it is My Father who gives you the true bread out of heaven.
John 6:33 “For the bread of God is that which comes down out of heaven, and gives life to the world.”
John 6:34 Then they said to Him, “Lord, always give us this bread.” 
John 6:35  Jesus said to them, “I am the bread of life; he who comes to Me will not hunger, and he who believes in Me will never thirst.
John 6:36 “But I said to you that you have seen Me, and yet do not believe.
John 6:37 “All that the Father gives Me will come to Me, and the one who comes to Me I will certainly not cast out.

The Lord declares that the manna given to Israel was a picture of Him. In the same way that a bread descended from Heaven to sustain the lives of the Israelites, now Jesus descended from Heaven so that He might become spiritual life for those who believe in Him. 

Because this picture is so important to the Lord, He has not repeated the manna provision since the time of the wanderings. He intends for the world to understand that the manna given Israel was a one-time provision, just as Jesus is a one-time sacrifice for the sins of the world. If the Lord continued to bring food from Heaven, the world wouldn’t understand the picture appropriately. 

Notice in John 6 the Lord rebuked the people for caring more about physical bread than spiritual matters. Likewise, we must not become focused on how God meets our earthly needs but remain centered on His provision for our eternal life in Christ. 

Furthermore, the Lord is capable of meeting the needs of His people in many different ways. Generally He supplies the saints with provision through natural means, including farming or food markets, etc., though He always possesses the power to grant a supernatural provision. In the end, we know the Lord will always ensure proper provision to those who are His children by faith, as the word says:

Matt. 6:25  “For this reason I say to you, do not be worried about your life, as to what you will eat or what you will drink; nor for your body, as to what you will put on. Is not life more than food, and the body more than clothing?
Matt. 6:26 “Look at the birds of the air, that they do not sow, nor reap nor gather into barns, and yet your heavenly Father feeds them. Are you not worth much more than they?
Matt. 6:27 “And who of you by being worried can add a single hour to his life?
Matt. 6:28 “And why are you worried about clothing? Observe how the lilies of the field grow; they do not toil nor do they spin,
Matt. 6:29 yet I say to you that not even Solomon in all his glory clothed himself like one of these.
Matt. 6:30 “But if God so clothes the grass of the field, which is alive today and tomorrow is thrown into the furnace, will He not much more clothe you? You of little faith!
Matt. 6:31 “Do not worry then, saying, ‘What will we eat?’ or ‘What will we drink?’ or ‘What will we wear for clothing?’
Matt. 6:32 “For the Gentiles eagerly seek all these things; for your heavenly Father knows that you need all these things.
Matt. 6:33 “But seek first His kingdom and His righteousness, and all these things will be added to you.

The Lord will not forget our earthly needs, Jesus says. We must keep in mind this promise is for those who seek His kingdom, as Jesus said in v.33. Unbelievers are also given a measure of mercy, but that provision is not assured, as we see around us in the world. 

For more in-depth teaching on the connection between manna and Jesus, please see our Gospel of John Bible study, particularly Lessons 6A, 6B and 6C,