Because ETH is a lot older and it's run by a snake called vitalik. 
ETH is not older. They are exactly same old. Since was same coin for more then a year. and shared same blockchain, that is now ETC blockchain. If we look that way, ETC is older since host the original blockchain, but practically they both share same blockchain till the moment ETH decided to go separate way.
I think you both have each one reason in something the chain at one time was the same but ETH first appeared on the scene, for example in the exchanges, for this reason one is older than the other,but I do not think that's the reason why the first is more expensive than the second,but rather I think because the majority decided to switch to the new chain that used the oldest name for the simple reason of supporting who designed the platform,since it is assumed that being supported by him would be more convenient for them.