To me, changelogs are never optional, just like we're not allowed to upload a mod without a description.
Then mod authors can add it to mod descriptions, sticky posts, mod file descriptions, or all of them as needed. Usually changelogs are in one of those places, but it's inconvenient when they're not in a place they should be. I know that changelogs in changelogs aren't effective for casual users, but leaving changelogs blank affects regular users.