And, honestly, if they came out with a statement that said (effectively), "Look, we're losing money here... we just _can't_ support free going forward. Here's our plan" that would be understandable. Sometimes you have a plan/goal, and you realize later that you were wrong and things need to change. But that's not what they did.
I disagree, there is always a way to keep it free, if you care about keeping your promises. Especially in this case where the service is essentially locally encrypted json blob storage. There’s already plenty of premium functionality not included. If you have runaway costs due to abuse, just make up new limits to solve it.