It's very possible to make a mystery box concept satisfying, you write the mystery before you start making the show and you don't let it extend wildly beyond the scope unless you create a new mystery that doesn't retcon the original one. A certain asshole made writing mystery boxes without worrying about how it was going to be resolved a huge thing and created a bunch of wildly successful but deeply unsatisfying shows and now for some reason producers think it's okay to write mysteries with no plan.