So thats the question.
What do i think about it? I think that it is expensive to build them even for galaxy empires or they have a small abount of human resourses = small amount of systems/planets = every empire have about 20-40 systems canonically.

A Design decision perhaps. Want lots of ships per Fleet? Perhaps try out another of the space based 4X's currently on the market that allows larger Fleet numbers. 4X game being withheld as it is, to some, bad karma to speak of other Games while in anothers Games Forum.  ;)  :) ;)