I don't follow Black Clover but my understanding is that the anime people want to go to more of a seasonal approach (think Attack on Titan). Right now I think they're too close to catching up to the manga, so if the anime just keeps going on then they run out of source material. I don't think it's because the manga is ending imminently.
Hunter × Hunter Hiatus × Hiatus is a bit of a special case because of how unreliable Togashi is. Just have a look at this chart: https://hiatus-hiatus.github.io/ There are a whole lot of missed weeks (red blocks) since 2006. We're on the longest stretch of hiatus ever right now