I think thats why the T-Virus ceased to be a thing in the RE universe, because one might ask "where is the T-Virus and why no one uses it anymore". The answer is simple, as a biological weapon, the T-Virus is obsolete. There are vaccines, cures, drugs and treatments for the virus at this point in the RE universe. You can easily get cured if you get to professional help in time. Hence why the T-Virus just kind of faded from the bio-terrorism scene, besides, zombies, compared to other BOWs, are rather inneffective as bio-weapons. They are slow, clumsy, literally brain dead and are only significantly dangerous on bigger groups.
It only got as bad as it did in Raccoon City because they didnt know what they were dealing with, but after that event, I think almost everyone knows what the T-Virus is and the zombies.
There are more powerful BOWs out there that you can use. Ironically, the T-Virus and Zombies became obsolete compared to the threats that came after, its almost symbolic.