Clearly, the background checks are missing things. Maybe they need to be done more frequently. Maybe they need to include accusations of improper behavior towards kids. Who knows. But that's the process that needs to change.
Sadly, I dont think the process can truly change.
In the end, background checks are based on public data. Arrests, charges, and convictions are public data. As a result, background checks of varying depths will uncover these types of information.
Accusations, whether founded, or unfounded, are not public information in and of themselves. As a result, background checks will not catch those.
In the end, arrests, charges and convictions are all based on something tangible and articulated facts. Accusations, however, can be made by anybody for any reason and do not have to be supported by facts. Thus, making accusations received by the police part of a public data base is unlikely to happen.
There could be privately maintained data bases that record information like: Youth Pastor "YP" or Coach "C" were previously booted from a church or youth team due to accusations of various sorts, strange coincidences, creepy vibes etc.
But, background check companies may be hesitant to link to these private sits due for accuracy concerns. They would know what arrests are based on, but dont know what "bad vibes", "strange coincidences" are based on, or if accusations were founded or unfounded.