Transparency It's not just about being sued. The chances of that happening are small, but if you were hugely successful you would want to ensure you were covered.
Webnovel could get a DCMA and your novel taken down.
And most importantly as writers were are artists. The last thing we want is some smuck stealing our work and posting on another site pretending it's theirs. So we should return the favour by respecting the artists who create the covers we use.