Matthew focuses on the question of why parables are being used, which focuses on the outside crowd, not the inner circle, while Luke focuses on the disciples lack of understanding. Mark's version is much more ambiguous saying,
4:10When he was alone, the Twelve and the others around him asked him about the parables. 11He told them, “The secret of the kingdom of God has been given to you. But to those on the outside everything is said in parables 12so that, “ ‘they may be ever seeing but never perceiving, and ever hearing but never understanding;
otherwise they might turn and be forgiven!’ ”
All I am saying is the synoptic accounts need to be taken as a whole, and to make a proposition based solely one one account is not the better part of wisdom. I don't necessarily disagree with what you have said, I just think you are being too narrow with the text because Matthew's account fits your argument the best.
Thank you for your kindness regarding my father! Just trying to make the best of a most difficult time. God is good!
Doug