So this is just a quick exploration of something I have noticed recently and that is the idea of a different number of episodes per season. There is a difference between different countries, but even in the USA there is a difference between series that sometimes seem arbitrary. It also can switch from season to season, one season is 24 episodes, another is 13 episodes and there does not seem to be an explanation why.
Part of this discussion is the idea of having filler episodes. There are plenty of series that have had to do various filler episodes that often slow down the story and really just seem to bore the audience. It is an interesting idea: do you try and fit in the required number of episodes, or do you try and tell a complete story? Some of it depends on the type of show I think, but there is still some level of how long can you stretch an idea out.