That's actually not true.

Imgur took their site down in the UK after they refused to pay a fine for monetising and improperly using kids data.

It's nothing to do with the OSA, but instead about Imgur not following data protection laws, although it happened at a similar time.

Imgur would implement checks at the drop of a hat, it's not expensive to add. They aren't being altruistic, they just didn't want to pay fines after they broke the law.