My monthly Hetzner bill is around €15000. I have been a customer at Hetzner for nearly 10 years. In the beginning I served traffic directly from Hetzner servers, but 4 years ago I switched to a caching system hosted at a different provider. Since then I have not received any copyright claims through Hetzner.
I can't think of a reason to cancel my account except that they want to free up resources for their own storage service. I am using a lot of disks and bandwidth. They might have been looking for a reason to kick me out and the launch of their own storage service could have been the final straw.
Keep in mind that the account cancellation mail arrived almost exactly one week before this announcement. They are keeping their lips tight about the reason of my account cancellation so I can only speculate.
That they don't communicate well with you really sucks, and I will read your blog post. But please stay on the sane side of reasoning.