I don't know. Maybe you're right. At this stage I think it's a moot point though -- why destroy Bitcoin when you can control it? And why advertise your power and risk losing everything?
Because you can't print bitcoins at will like with fiat money. They want to protect their power to print money at will and defend their privileges. Destroying bitcoin does this and about losing... what, some millions of $? They have hundreds of billions!
Note that while controlling the majority of the Bitcoin network does not allow you to print Bitcoin, it allows you to raise fees arbitrarily. For example, you could stop processing transactions with a fee lower than 1 BTC.
So the evil master plan would go like this:
1. Invest in enough computing power to control the majority of the network, you control the blockchain now.
2. Stop integrating blocks mined by others in the blockchain.
3. Stop including transactions with a fee less than X, forcing users to give larger fees.
4. Earn lots of transaction fees.
5. Invest transaction fees into more computing power in order to keep the majority.
6. The other miners will starve one by one as they won't be able to earn anything anymore.
7. Bitcoin is now a monopoly which you own.