The reason to buy the coin is that smart contract operations all require ether (gas?) token. That's the cost you pay for the "Ethereum virtual machine" to run your computation.
Discussion
Cool. But why? it's almost like it's creating a problem to solve the solution with their technology.
Well the idea of Ethereum (at least originally) was to create an uncensorable "global computer." So the token having value is necessary to provide the incentive for the miners/validators to actually run the code.