Dissertation papers are rather hard things, especially if you have to write at least one of them. Nevertheless, even if dissertation papers are so difficult, every year hundreds or thousands of students present their dissertation papers in order to get master degrees and PhD degrees.
As for Master degrees, quantity of master dissertation papers is bigger than quantity of PhD dissertation papers because it is more difficult to get PhD degree than Master degree. Master degree is usually received by students after five years of studies at university or college. In general, students prefer to get complete higher education. That is why they choose to get Master degree after Bachelor degree. As for PhD degree, it depends upon students. Usually this degree is received by students who want to work in the sphere of education or to be tightly connected with the sphere of sciences. These two areas require the presence of PhD degree in order to be able to carry out important experiments and researches or to teach at higher educational establishments. So, it is understandable why the quantity of PhD degrees is not equal to quantity of Master degrees.
As for dissertation papers, both academic degrees require writing dissertation papers. It is obvious that PhD dissertation paper is more difficult than master dissertation paper, because levels of two degrees are different. If PhD degree is higher than Master degree, then the level of PhD dissertation paper should be higher and higher level presupposes the bigger complicacy of the dissertation.