Right now the cost in electricity and computing power to maintain the blockchain is just not adapted to more scale.
When will crypto-currencies massive mainstream breakout out happen?
Ouriel Ohayon
41310

I may be mistaken but I think that Bitcoin is expensive to process by design. The cost of electricity is one reason why the blockchain is resistant against attacks. If the math was simpler it would take a lot less electricity but it would also make it vulnerable to attacks. And this is necessary due to the decentralized design; it imposes a barrier of entry in the system.

I don’t see any easy way out of this. If the mining were to be made less expensive, there’s a huge risk that lots of people would immediately start mining right away, accelerating the network but causing supply problems – perhaps some inflation, despite the design being based on a deflationary model. It’s a very delicate balance.