Why Can't All Seed Grow and Bear Fruit?

This passage bothers me:

"Lest at any time they should be converted." Mark 4:12

Doesn't the Lord want all to be saved? Here's a thought from Jon Courson to consider:

"Why would Jesus teach in such a way that truth would be concealed? Simply because He will honor the wishes of every person. Therefore, if a person does not want to see, the Lord won't force His way upon him."  Jon Courson
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Considering the larger context of this parable through the eyes of MacLaren has also been helpful:

"Luke is particular in dating this parable as spoken at a time when crowds resorted to Jesus, and the cities of Galilee seemed emptied out to hear Him. No illusions as to the depth or worth of this excitement beset Him. Sadly He looked on the eager multitudes, because He looked through them, and saw how few of them were bringing ‘an honest and good heart’ for the soil of His word. Just because He saw the shallowness of the momentary enthusiasm, He spoke this pregnant parable from a heavy heart, and as He tells us in His explanation of it to the disciples (ver. 10), uses the parabolic garb as a means of hiding the truth from the unsusceptible, and of bringing it home to those who were prepared to receive it. Every parable has that double purpose of obscuring and revealing. The obscuring is punitive, but the punishment is meant to be remedial. God never cheats men by a revelation that does not reveal, and the very hiding is meant to stimulate to a search which cannot be vain." -Alexander MacLaren

Our natural state:

"And you were dead in the trespasses and sins in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience— among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind." Ephesians 2:1-3

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The Word, even when rejected, is not of zero effect:

"The gospel rejected or perverted does not lose its power, but now goes right on in driving the soul into deeper rebellion and hardness." -BI

And, it must start with the Word:

The Spirit operating upon the heart apart from the Word would be only to give a vague inclination without an object as its end and purpose. And therefore all religion that does not spring from the seed of God’s Word is a dim abstraction of an unreal sentimentality. It is aimless and powerless, the continual ploughing and harrowing of a field without putting any seed into it.