[s1artibartfast]

Good question. Take many many antibacterial molecules to kill a bacteria, so there are two plausible methods. The first is that two compounds can have different pharmacokinetics. That is to say, they move through the body in different ways and have different concentration profiles.

The second is about how they are used. Two separate compounds with the same pharmacokinetics could be effective if you use them in parallel, but you have to contend with the fact that real human users may not always use them that way. If two different companies make compound a and compound B, it is virtually impossible to prevent someone somewhere from using them separately