There's been a change in the way doctors think about meniscal tears these days. Studies show long-term problems occur when the meniscus is removed. For a while they were repairing the tear. They did this by shaving off any frayed edges and stitching it back down to the bone.
More studies showed even this wasn't needed. The meniscus seems to be able to heal itself better when left alone.
Repair isn't needed if the tear is "stable." Stable means the torn piece doesn't move around, flap over, or get stuck inside the joint causing clicking, catching, or locking. The doctor can test this by using a probe and trying to move the injured meniscus.
Usually tears in the back half of the knee are stable. Tears smaller than one cm are also more likely to remain stable.