Why was the last episode of PowerPuff Girls unaired?

The last episode of The Powerpuff Girls, titled "The Powerpuff Girls Rule", was not unaired. It aired on March 31, 2005, marking the end of the original run of the series.

There seems to be some confusion, perhaps stemming from the fact that there were multiple Powerpuff Girls shows, including a reboot in 2016.

The original series had a total of 78 episodes over 6 seasons. The final episode, "The Powerpuff Girls Rule", is widely available online and on streaming services.