In Star Wars, one of the most prominent ways of expression is through one's lightsabers. Since A New Hope, numerous hilt types -- from double blades to cross guards -- have been seen. However, none compare to the unique and imposing design of the Inquisitor's lightsaber. Used by Sith Inquisitors, these hilts could be a single or double-bladed weapon and spin without the need to twirl. However, this left the hilt open to a major design flaw that more often than not led to their users' deaths. Even with its flaws, the Inquisitors still utilized the weapon.
Sith Inquisitors were users of the Dark Side who never obtained the full teaching of its methods. However, they were malicious and act like secret police for Darth Vader, capturing any surviving Jedi after Order 66. When their leader, the Grand Inquisitor, faced off with Kanan Jarrus and Ezra Bridger in the Season 1 finale of Star Wars Rebels, he met his match when Kanan used two lightsabers to cut the spinning ring in half.
The hilt's also susceptible to damaged emitters that lead to a total dismantling of the hilt when used for flight by Force-sensitives. This was how the Fifth Brother died in the Season 2 finale of Star Wars Rebels. While these faults should've been enough for Inquisitors to change their methods, there was a canon and real-world explanation for why they were still in use.
In terms of the canon, the Inquisitors were using the lightsabers after their weaknesses were exploited because of intimidation. Many of the Jedi that survived Order 66 were younglings whose masters protected them. Because of their lack of training, they didn't have the proper techniques to help overcome fear. As a result, it was easier for an approaching Inquisitor to terrify an inexperienced Jedi with nothing but a black outfit and spinning double-bladed lightsaber.
The ruthlessness of the Inquisitors also played into why the lightsabers maintained prevalence within their ranks. For example, in Star Wars Jedi: Fallen Order, Cal learned enough from his master to help face his fears, but facing off with the physically imposing Ninth Sister served as a massive challenge for the Jedi. To make matters worse, she and her fellow Inquisitors had no qualms about taking innocent lives to achieve their goal. This was proven when the Second Sister killed Cal's friend, Prauf, to lure him out.
When discussing the real-world reasoning for why the lightsabers were never changed, the answer is likely aesthetic. Each Sith in Star Wars had a unique lightsaber style that separated them from their contemporaries, and the Inquisitors were no different. They showcased how they were less skilled in combat than those who didn't need a spinning hilt while also showing how their fear factor made up for that. They also offered a perfect opportunity to create toy replicas that kids could buy while featuring a function unlike any other lightsaber before.
The Inquisitor lightsaber has since become one of the more unconventional designs in Star Wars. Unfortunately, its major design flaw doesn't place it in any top spot for reliability. However, its intimidation factor and merchandise opportunity prove that there's still a high level of value in the hilt design. Despite this, when facing a Jedi, the Inquisitor lightsaber is more of a death sentence than a protective weapon.