There's a difference between the amount of energy "required" to mine Bitcoin and the amount of energy being spent to mine Bitcoin.
There's currently a "gold rush" in Bitcoin (and cryptocurrency in general) where there is a lot of energy being spent in the hopes of striking it rich.
As Stoic Joker mentioned, it is relatively inexpensive to get starting mining Bitcoin, so the economics of it naturally results in a fairly balanced system where costs to mine nearly equal profits earned. When it becomes more profitable, then more people start doing it. When it becomes less profitable, some people shut down their miners. It's simple supply and demand, with relatively little cost of entry or exit.
There is nothing in Bitcoin that requires energy consumption mining it to be so high. That is just a natural side effect of the current (or prospective) profitability, fueled by the greed inherent to human nature.
Technically speaking, one could mine Bitcoin on a Raspberry Pi. The proof of that is the fact that when it first began, it was just a few people running the software on their old laptops nearly 10 years ago. And indeed, under the right circumstances, the network could easily survive on a network of hundreds of RPis (or less) instead of the huge multi-million dollar ASIC operations we currently have.
A system that gives you a reasonable shot at gaining new BitCoin is going to cost you. You still need many GPUs, preferably a motherboard with enough PCI lanes to properly support these GPUs, a processor that can support those lanes as well, a power supply that can support this setup, a case that allows for all this equipment to be mounted in and you will be needing an airconditioned room to put this contraption in. Several thousands of USD such a system will cost you. Still nothing compared with actual mining equipment.-Shades
This is a few years out of date. It's senseless trying to mine bitcoin with GPUs (just as it is senseless to try mining bitcoin with a RPi). The Bitcoin world has moved on to ASIC mining.