Sam does apologize to Dean in the s 11 episode... Love Hurts I think.
I think Kripke AND gamble's goggles are why Carver focused his story arcs the way he did. He deliberately had Sam make similar mistakes as fully human and then admit his mistakes and atone for them still fully human.
This left Dean with the supernatural arcs which was fun even if the character growth was largely about Sam admitting he made a mistake, treated Dean badly, caused an Apocalypse. We saw Sam feel guilty! We saw Sam apologize! We saw that Sam was shi#$ to his imaginary friend and he finally apologized to Sully too!
IMO Carver was smashing the previous showrunners' Sam goggles.
Then Dabb came along and was terrible starting with Red Meat.