You are expected to have a cover.
The audience expects a certain degree of ... professional ... from the amateur writers, which includes, but isn't limited to, procuring a cover for your novel.
Where would you get such a cover is the entirely different matter...
If there wasn't the "AI" you would simply download the pictures you like from the Internet and call it a day (something the artists often forget), but you wouldn't leave your story without the cover if the site allows one to be uploaded.
Of course, there are sites which don't allow for covers, such as AO3, but that's because they realize that the covers create another layer of IP infringement for them to worry about.