Cryptocurrency mining, which used to be a “solo” activity, has become so difficult and so expensive that it has been taken over by high-powered “industries” – groups that have a large investment in hardware and can either afford the electricity or have access to really cheap power. It is nearly impossible today for the individual miner to solve the increasingly difficult “puzzles” and earn the token rewards.
https://thenextweb.com/contributors/2018/01/02/blockchain-can-lead-better-ai-products/
It's a shame as this seems to go against the whole ethos of the blockchain being decentralised and for the people.