Why can't a user edit their own comment on a blog, but they can on nearly every other content type?

Why was this 'by design', and why isn't it a 'toggle-able' option rather than a hard limit?

We have members complaining that they can't edit their comments, and we can't even toggle it based on a permission change.

Having to raise it as an idea before it's changed only frustrates members in the meantime.