Not necessarily, take for example Emperor Palpatine from Star Wars. He is objectively evil, and he doesn't have a traumatic backstory nor compelling motivations, but he's still super popular and iconic, because he has a badass design, an entertaining personality, and all around a lot of presence in the storyline. He only appears in the final movie of the original trilogy, but he was always present in a way, as he was the puppet master behind Darth Vader (there is a scene in episode V where Vader literally kneels before a projection of Palpatine). He's so beloved yet at the end of the day he's just a crazy lunatic who wants to rule the galaxy as an eternal emperor.
And if you don't believe me check any reaction to the trailer of Episode IX on youtube, the crowds went absolutely crazy once they heard that chuckle at the end.
Same thing here, you don't need morally grey motivations to be a good villain. It's easier to make a decent villain if you give them understandable motivations, but not necessary.
Also what is very important for a villain is design. A villain needs to have a cool design that reflects their personality and powers. The Jailer right now looks very generic. I preferred him as that "Evil Aman'thul" from the Shadowlands teaser. He looked more mysterious and mystical, you could say.