For those who don't know Trigon was the main villain of several story arcs in the Teen Titans series than Deathstroke who later get his own series and becomes more of an anti-villain. Also cuz Trigon is the more powerful and evil of the Titan's rogues gallery there is that.

You Guys do realize that Deathstroke in the comics is a mercenary and only the main villain three times? While Trigon is has been the main villain more times than Deathstroke did. Also Deathstroke also had his own series.Also let's face it Trigon is more powerful than deathstroke.Also Cuz Deathstroke is an anti-hero/anti-vilain and was always used as a minion for the other villains.

Wow deathstroke is more popular huh? Well don’t you guys realize that he is more anti-hero/anti-violin and a villain protagonist these days? Also deathstroke in the comics is a mercenary and a right hand enforcer to anybody Trigon was again the main villain for every story arc he appeared in.