If you have a KvK in The Netherlands your PII details are public, and you will start receiving physical spam from companies despite such spam not being free to send. I never receive spam from individuals though; only companies.

On top of that, the costs of electricity are not the same everywhere (they are very expensive in The Netherlands, for example, than in the USA, and China is very cheap). Nor is it widely stable available everywhere (examples include India and Africa). Proof of Work is basically a waste of energy as well.