Originally Posted by
Leancarp900
In this case, it's probably mainly because it's easier to make a Suicide Squad game (which is basically just a third person shooter) than a Justice League or a Teen Titans game. Also, this likely got greenlit in 2017, very shortly after the success of the first movie. Gunn was also the one who chose to do Suicide Squad because he is a big fan of Ostrander's run. It wasn't forced upon him by Warner or something.
That being said, yes, somebody at Warner really thought the Suicide Squad was gonna become a big DC franchise. That's evident by the fact that there had been a Suicide Squads movie in development since the late-2000s, that early pitches for the JL movie back in 2011 or so included the Squad, their appearance in Arrow and that WB Montreal also had a Suicide Squad game in development at one point teased at the end of Arkham Origins. This is all very strange for a franchise that not many DC fans would have considered a major one prior to the New 52. My guess is that Warner saw how popular certain DC villains were (Joker, Harley, Deathstroke) and they thought it might be a good idea to try to capitalize on that.