You are binge-watching too much Tv series and there are many seasons of a specific Tv series. Expanding these series with the extent of limit could be backfired and it could be the worst move by the producers.
There are reasons to Justify the fact:
Tv series should be short and precise so that the users don’t spend too much time on their devices. This makes people addicted to it and it leads to such cases of insomnia among teenagers. So the story build should be user-friendly and interesting and don’t seems boring. As recent cases show that some users left watching popular Tv series like Game of Thrones because due to getting bored.
Expanding seasons without any definite script planning could make a hit series a disaster in a season. So expanding doesn’t work all the time and it’s a gamble for producers. Expanding will only be successful when the plot remains elements of surprise for the next season. Unless it mostly failed and criticized by the fans.
Expanding season mostly requires a wide no of actors in the series, as a resultant focus on characters been divided. Multiple characters ruin the impact of a character who’s been running the show since the beginning. Taking the example of the flash, for expanding they have to make crossovers to run the show which features the arrow characters. This will make the show exciting at some point but not work every time.
So expansion has its advantages but excessive becomes a kind of stretching a series which make fans confused and irritated.