There are three kind of resources in EOS system: RAM, CPU and NET. When creating an EOS account, all these resources will be used.

 

  1. When creating EOS account, 4KB RAM will be consumed.
  2. The creator will stake certain amount of EOS for CPU and NET resources for the new account.
  3. These staked EOS are transferred to the new account.

 

For the reasons above, it needs to consume EOS for registering.