When the blockchain was introduced one of the main ideas was to make it impossible for anyone to manipulate it. If funds where stolen or lost they were lost and there was no way to recover it. Even not as Mt Gox collapsed and thousands lost their money.
Back then is issue was that Mt. Gox was running on complete rubbish servers and code that was handling all transactions.
Now a new star came around : Ethereum.
They wanted to do everything differently, more efficient and better then Bitcoin.
But when the Dao used Ethereum to run its decentralised code quickly researchers and coders discovered a bug or coding mistake that could jeopardise not only The DAO but also Ethereum everyone said that it will be fixed but for now its better to put more money in.
Even the big names of Ethereum put lots of their funds into The DAO.
And then all of a sudden the unbelievable happened someone smart enough used the coding error to get access to the money.
Buterin and friends saw that their money got stolen buy someone who has been smarter so they wanted to get back their money.
Unfortunately this was only possible by breaking the laws of the blockchain and changing it.
Based on their power and their greed they managed to hardfork the blockchain.
According to them they had people voting on if they should hardfork it but only ~20% of all miners took the vote and voted for the hardfork.
Now that Ethereum Classic gains momentum Buterin and friends realize that they had no clear majority to hardfork the blockchain and that they lost.
Not only in value, ETH dropped from $14.40 to $10.96, but also in Hashpower - more and more people move away from Ethereum and put their hashpower and money into ETC which continues to operate the old chain.
This is a clear sign to everyone:
Don't mess with the laws of blockchain and manipulate it