Well, it doesn't make sense to scale the main chain in that sort of way, because you'd be looking at blocks the size of several terabytes in order to fit in global scale transactions. And so running a node would then require you to basically run a data center, which wouldn't make the system decentralized at all.
Electricity for mining is also not directly related to transaction throughput. Mining is the arbitrage of bitcoin price and electricity/mining hardware cost. The system technically does not need more electricity to secure the same amount of transactions. What happens is when bitcoin's price goes up, so does that arbitrage value, giving mining a profit incentive.