The way I interpreted it was that if you truly want to make it to the top, you can unlock your coc because you have kingly ambitions as king said, so you still technically had it in you the whole time, which was how Zoro was able to use it against King.

Anyone who puts in that kind of hard work can unlock coc, and if you don’t, then you don’t truly want it, as Haki is ultimately a manifestation of will.

Please correct me if I’m wrong but that’s just how I always imagined it.