This is a great cactus! Generally when a succulent has not put off deep roots, it’s a sign that it is not being watered deeply enough.
When watering, make sure you are completely soaking the soil (using a well draining soil). If you think of cactus in the desert, they get flash floods of water and then long periods of drought. Your cactus needs the same.
The well draining soil is important because you don’t want the plant to sit in water too long. It needs just enough time for it to absorb the water it needs and then start putting off strong healthy roots as it searches for more. If the soil remains wet for too long, the roots can rot.
Cactus have a thick trunk full of water so they can tolerate long periods of drought, but they will thrive with more water. If you use the soak and dry method, only watering when the soil has dried out completely, you’ll find it will put off deep healthy roots in no time!