Because gamma knife will blur the boundary of tumor, it is more difficult to operate again.
Moreover, the growth rate of meningioma is slow, and the average person may not grow obviously or only a little after a few years, unless it grows in a special place, there will be no symptoms. Otherwise, surgery is not recommended. Generally, it is called observation first, and the symptoms are being solved.
After all, brain surgery is no more risky than others, whether it is gamma knife or surgery.