Effectively monetizing the hosting of images embedded elsewhere seems like a fool's errand—at best, it's possible to subsidize that usage with other revenue streams. The vast majority of people wanting to post images on forums have never financed their posting and the communities themselves haven't managed to either. Photobucket and Tinypic left a lot of litter on forums that survived their era, and Imgur will ultimately do the same.
It seems a bit like they're saying: "ohhhhh, did you people think we were an image hosting site? Heavens no, we're an SNS and always have been. We'll update our rules to clarify this".
They were image hosting for reddit. Once it was obvious reddit would kill their only use case soon, they became a social media platform. A better idea than simply dying. Every platform now has its own image hosting so their service was rapidly becoming irrelevant.
The big ones do. There is stil the long tail of forums and legacy chat platforms that don't do hosting or have extreme limits. That is what will be most affected by this change.
