What exactly was predictable about it ?
What was predictable was that if Bitcoin ever 'took off', mining it would require ever-increasing processing power - and therefore ever-increasing electricity use. The knock-on effects of this were also quite predictable.
But why must increased processing power equate to increased electricity usage? Because
Moore's law is dead.
Moore’s Law is named after Intel cofounder Gordon Moore. He observed in 1965 that transistors were shrinking so fast that every year twice as many could fit onto a chip, and in 1975 adjusted the pace to a doubling every two years.
The chip industry has kept Moore’s prediction alive, with Intel leading the charge. And computing companies have found plenty to do with the continual supply of extra transistors. But Intel pushed back its next transistor technology, with features as small as 10 nanometers, from 2016 to late 2017. The company has also decided to increase the time between future generations (see “Intel Puts the Brakes on Moore’s Law”). And a technology roadmap for Moore’s Law maintained by an industry group, including the world’s largest chip makers, is being scrapped. Intel has suggested silicon transistors can only keep shrinking for another five years.
Chip density doubling every 2 years? Doesn't sound that dramatic, but in just a few years that geometric progression has given us computers with a
million times more transistors in them. To someone like me who was playing around with computers that had only a few kilobytes of RAM, the idea that I would be using a PC with Gigabytes of RAM in it was ludicrous - and yet Moore's Law had already predicted that this would happen.
But Moore's law is failing. A modern high-end CPU or GPU is vastly more powerful than the chips used in early PC's, but also uses a
lot more power. The ever-shrinking transistor size was helping to keep power consumption down because smaller transistors can operate faster without using more electricity, but it could not keep up with the insatiable demand for more processing power.
The ever increasing processing power (and therefore energy input) required to mine Bitcoins is not a bug, it's a
feature which its inventor and anyone who understood how it worked was well aware off. What they were perhaps not aware of - or chose to ignore- was the
scale. I suspect most early bitcoin users either didn't do the math, or were unable to comprehend it - mining Bitcoins on the their PCs and thinking, "If these things take off I might need a more powerful PC", but not considering that when the price hits $1 million due to widespread adoption they will be competing against billion dollar mining pools sucking power directly from hydro dams. But if Bitcoin was to fulfill their dreams then this development was inevitable - and totally predictable.
How widely used Bitcoin will become may not be predictable, but the amount of electricity it will use when it gets there
is. Market theory tells us that the 'industry' will find ways to lower its production costs, which in this case means getting cheaper power. So 'miners' will go to locations where they can get it (ie. China). And since mining is a business not an ideology, they don't care if it's cheaper due to government subsidies or slave labor or any other 'immoral' reason (even theft, if they can get away with it).