There might be an obvious answer, as I've only been using Radarbox for about a week the large number of inaccuracies regard flight data became quickly visible so I have been wondering what the reason is.
According to the official documentation on the flight
data page getting the information in bulk shouldn't be an issue. However there seems to be a constant need for users to provide manual database updates.
As a provider that sells access to its API meant for businesses, the need for the information to be accurate should be a given. For a casual aviation geek like me with an interest in flights as a hobby it's not as important.