When you kill (or infect) about 95% (or more) of the world's population, and the same virus can infect animals, well, you are doing something wrong. Now, why do you need more powerful monster?
Why do you not use all of your resources to survive this apocalypse? The guards and scientists may have family. If when you have unlimited resources you can't do good things with T-Virus, now that the things are more difficult, you can't continue doing the same things. Why do they continue doing experiments?