Depends on how much effort is shown to have been made by these app stores to prevent malware. For example, if Steam shows significant cases where malware games

Depends on how much effort is shown to have been made by these app stores to prevent malware. For example, if Steam shows significant cases where malware games have been removed, and can prove they actively work to remove these cases, then it won't be much of a problem for Steam. They are doin their best.