That is because it was discovered that the D-shape tokamak was more stable than toroidal ones. All of the major ones since the 80s have used the D-shape.
The D-shaped "advanced tokamaks" and spherical tokamaks are similar shape but the spherical has smaller center hole. That is the most efficient but it is harder to build. The center hole is the most confined space in giant ITER.
The D-shaped "advanced tokamaks" and spherical tokamaks are similar shape but the spherical has smaller center hole. That is the most efficient but it is harder to build. The center hole is the most confined space in giant ITER.