In cube strength of concrete testing why only 150mm*150mm*150mm cube is used....why not the mold of other dimensions are used?

I think that this is because many experiments was done in the early times. and they found that size to be suitable. then all testing equipments are designed to test this size. If you want to test another size you should use a unique testing equipment. another question is why bricks are in this size ? I think that the answer is the same even for the different sizes of bricks