According to Kolb, it all goes back to the injury itself. Because it involves broken cartilage on top of the broken ribs, they're recovering faster than the cartilage and can't fully heal until everything around them heal.
"Whenever the cartilage broke, (the ribs) are laying underneath my sternum. That's how they are trying to heal, rather than healing where it's butted up straight against it like a normal cracked rib, flush with each other, mine are laid underneath there. That's what extends the process."
Some have questioned Kolb's ability to actually come back and play this season and, given his description of the healing process and him saying he's not completely there yet, those concerns don't seem totally off base.
That being said, Kolb is still adamant he's going to return, but says he wants to take his rehab slowly. With these kind of injuries, that's always the smart bet, because they have one of the highest rates of re-injury if not treated with caution.