For example, Japan, Germany and some other countries have governments organized into a small number of bodies Whereas Canada, Indonesia, Pakistan, and other countries have many.
And considering the relative size of the population and economy between Japan, and Canada for example, the government of Japan is vastly more concentrated. So much so that it should be clearly noticeable, so it doesn't seem like it could arise by coincidence.
What are some of the theoretical and practical reasons for either?
14 Ministries and ministry level agencies
~16 Ministries (not sure)
37 to 39 Ministries and ministry level agencies (depending on how it's counted)
~34 Ministries and ministry level agencies (not sure)