Because he could satisfy and control emma from the start...
8 year lolden was running around with emma just fine. He was giving it enough coa that it never had to suck out his coc.
But zoro can't do that currently. Fact of the matter is, zoro doesn't even know he has coc Or acoc. So the only reason he can use acoc is because emma draws it out for him.
This is undeniable as of this chapter
This chapter destroys the enma power agenda, again. It was foolish back then and it's worse now. It's time for that agenda to die
Gaban and Luffy told us Zoro has CoC. That is now four people who stated Zoro has CoC. None of them said it was because of enma.
Oden's father explained to us how enma works. The sword works by forces the user to release CoA haki. He didn't say anything about releasing CoC.
Every single time we saw Zoro lose control of enma and it forced him to release haki only CoA haki was released.
Just because Oden could use enma at 8 years old when he's not using haki doesn't mean he has mastered enma.
There's no signs he using haki.
Zoro had no problem using enma when he wasn't using haki.
Just because Zoro didn't realize he was using CoC/ACoC doesn't mean it's because of enma. Zoro was controlling ACoC haki against King. He just thought he was still using CoA.
Here Zoro releases overwhelming haki and then release ACoC haki.
He's controlling the power separately.
Here he just release ACoC haki to counter King's attack.
That's not even enma, that's the demon slayer. Enma doesn't effect other swords.
As I said earlier, this is just Oda poor writing to stop Zoro from overshadowing Luffy. Zoro obtained the same power as Luffy much faster.