This article kind of gives us a little more clarity why WB isn't delaying this for a couple of months. Nolan is the one pushing really hard for it to be the first film back in theaters and the studio is trying their best to keep their golden child happy.
Christopher Nolan is reportedly hesitant to delay Tenet's release by months because he wants to show faith in movie theaters.
www.slashfilm.com
I can see where Warner Bros is coming from though. In its current release date, analysts are currently predicting that the film will only pull in a $30 million domestic opening weekend. Since Nolan reportedly has a deal for 20% first dollar gross, he'll come out of this making money regardless of how it performs. But with a $200+ million dollar budget (for a non-franchise film no less), those kind of numbers would be a bloodbath for WB.