In comparing Isaiah 6:10 with Matthew 13:13-15, the Isaiah passage states actively hardening the hearers:
"Make the heart of this people calloused;
make their ears dull
and close their eyes." (Isaiah 6:10)

It seems the Isaiah passage is more devastating a judgment against Israel. It isn't preceded with explaining the parable of the sower, and it doesn't offer "whomever has ears, let him hear"

It seems the audience was past the gracious point of receiving and hearing a cautionary warning of not hardening their hearts.