Summary: Do Christians seek comfort? Or do we seek substance? Jesus offered substance, but it wasn't always appreciated, even by those identified as disciples.
“When many of his disciples heard [Jesus’ teaching], they said, ‘This is a hard saying; who can listen to it?’ But Jesus, knowing in himself that his disciples were grumbling about this, said to them, ‘Do you take offense at this? Then what if you were to see the Son of Man ascending to where he was before? It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life. But there are some of you who do not believe.’ (For Jesus knew from the beginning who those were who did not believe, and who it was who would betray him.) And he said, ‘This is why I told you that no one can come to me unless it is granted him by the Father.’
“After this many of his disciples turned back and no longer walked with him. So, Jesus said to the twelve, ‘Do you want to go away as well?’ Simon Peter answered him, ‘Lord, to whom shall we go? You have the words of eternal life, and we have believed, and have come to know, that you are the Holy One of God.’” 
“Sell the sizzle, Not the Steak,”  was a concept coined in the 1930s by legendary ad copy writer, Elmer Wheeler. Stockbrokers, sometime during the 1980s, again employed the term as a means of promoting the financial products they marketed. These marketers reasoned that people would be motivated to buy based on excitement rather than basing their purchase on facts. Marketers could build demand for a product through advertising. What is important to note is that marketers were not selling the product itself! They were building demand for the product. By selling the sizzle, almost anything could be marketed.
The crowds that followed Jesus wanted sizzle—He offered them steak. Perhaps those people would dissent from that characterisation if they were around today, but the evidence is pretty clear. Jesus’ teaching was not welcomed by the masses following Him. So long as Jesus performed miracles, made listeners feel good about themselves, rebuked religious elites or spoke parables that were not always understood, the crowds loved Him.
Nothing much has changed in the intervening centuries; contemporary church goers are still motivated by excitement. Solid meat is far less exciting to the average church goer. In rejecting the meat of sound teaching, contemporary disciples prove they are spiritual descendants of those who clamoured for Jesus to perform a miracle or to entertain them with a sign.
Choking on solid food is not a new phenomenon. A missive penned to early adherents of the Faith contains a stinging censure. After speaking of Christ’s kingship, an ancient writer penned this assessment of his readers, “About this we have much to say, and it is hard to explain, since you have become dull of hearing. For though by this time you ought to be teachers, you need someone to teach you again the basic principles of the oracles of God. You need milk, not solid food, for everyone who lives on milk is unskilled in the word of righteousness, since he is a child. But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil” [HEBREWS 5:11-14].
Contemporary church growth experts promote techniques guaranteed to grow a congregation; and church members are notorious for demanding leaders who will “grow” the congregation. Church growth experts, whether consciously or unconsciously, are training church leaders to sell the sizzle. If the pastor is unable to make the church grow, the congregation can fire him and hire someone who will do whatever is necessary to make the church grow. After all, church growth is more important than the spiritual growth of disciples. This makes it easy to imagine the pressure pushing pastors to perform according to the expectations of parishioners. What is important to the average church goer is the excitement generated in the service. Something to make her feel good about being part of divine work will surely keep her happy.
“WHAT HE SAYS IS HARD TO ACCEPT. WHO WANTS TO LISTEN TO HIM ANYMORE?”  The English Standard Version that I use translates the response of the crowds literally, according to what John wrote. Other translations, attempting to capture the thrust of what was being said, point to the refusal of the crowds to listen any longer. So long as Jesus performed miracles, or delivered sermons that attacked the religious elite, the crowds were enthusiastic. However, when Jesus called for devotion to Himself, they were insulted. As God’s Word translates their response, they argued, “What He says is hard to accept. Who wants to listen to Him anymore” [JOHN 6:20 GOD’S WORD]? “Who wants to listen to Him anymore?” Imagine!