I'm not sure why it was ever closed. Devs fixed boosting by prohibiting kills in areas where the player count was high. They could have simply introduced that same idea into CTF if boosting was an issue. If there was a glitch, it may have been exploited like 4-Lom said.
Someone needs to explain to me how CTF was. I haven't been around that long. Was it like what others have been doing in their homes with the vases and respawn thing from castle?