They had a contractual agreement w/ MCS Holdings which almost certainly said they wouldn't do something like this. Since they did, CNNIC can say "they promised they wouldn't" and absolve themselves of responsibility.
Of course, MCS Holdings can then just change their name or create a new company or whatever, get a new agreement (with CNNIC or another Root CA) and continue on.
If CNNIC decides it wants to rent out their trust bits like this, they need to realize they are putting their trust on the line. Any actions performed by sub-CAs under their trust authority should be their responsibility. They need to re-evaluate if taking money to rent their CA bits is worth the stakes.
The alternative is that it's a free-for-all for everyone in the trust store. Cash in selling sub-CAs and shrug if they get caught? Really?
Of course, MCS Holdings can then just change their name or create a new company or whatever, get a new agreement (with CNNIC or another Root CA) and continue on.