Supergirl is remained in The CW's lineup mostly thanks to the show's format, which is entirely fitting to the network's superhero row. Nonetheless, also worth noting that the viewership of the series is dropping from season to season. The current season premiere has garnered 1.523 million viewers (0.45 key demo P18-49), which is 18,43% lower versus the previous season.
On the other hand, Supergirl S4EX09 has drawn 2.167 million viewers with a 0.77 demographic indicator (+72.39% and +119.32%, respectively). It's not clear how long the series might remain in The CW lineup. Yet you should know that Arrow is being canceled after Season 8 because of low viewing figures.
As you remember, Supergirl moved from CBS, where the show drew 9.81 million viewers during its premiere. Therefore, The CW was ready to see the decrease in the viewership since the network itself is not comparable to such a giant as CBS. Yet still, television ratings serve as a key indicator in the decision on renewal or cancelation of a series.
Furthermore, a reception of the current round of Supergirl was a bit controversial. According to the data presented by Rotten Tomatoes, Supergirl Season 4 holds a score of 7.54/10 and a 90% approval rating among critics, while the viewers have rated the current season at only 2.5/5 (41%).
Summing up, we are concerned about the future of Supergirl. We are happy that The CW opted to renew the show for Season 5. Yet we believe that the team, which stands behind the television project will have to work harder, if they want their superhero series to remain in The CW's lineup.