Because the real world is far less sterile than in a laboratory. People come and go, UV exposure is a factor if outdoors (this was shown to play a huge role in rendering the virus inert, which is what fueled the outdoor dining surge during the height of the pandemic), and there are all kinds of surfaces that have some amount of anti-microbial properties as well. It's why doorknobs in hospitals were historically all made with brass (and many still are), because the copper content helps kill germs that get transferred to the knob as people open and close the door. The same goes for push plates on doors without knobs, railings in bathrooms and stairwells, and other common surfaces like cabinet handles. Stainless steel has taken over due to being cheap and easy to clean, but it's not the same in terms of killing stuff that's living on it the way bronze does. That said, there's research being done on ways to passivate steel (inhibit corrosion) using copper containing ions, to such a degree that it transfers this capability to the steel. Copper is already used in some bluing solutions for steel, but you'd probably need to use a lot more applications of it than you would just to blue the steel properly.