The courts can choose not to impose a ban if they think it would cause exceptional hardship, but they must ignore any circumstances which have already been used to avoid a totting ban in the last 3 years. So while in theory there's no limit to the number of times you can avoid a ban, in practice you'd have to have a lot of very unusual circumstances to do it more than once or twice and to rack up more than 15 or so points and keep your licence. And contrary to popular opinion, magistrates tend not to be completely stupid...
So I suspect that most of these cases are either (a) admin/IT cock-ups where the court hasn't been aware of the diver's History
or (b) someone who commits a lot of offences in a short time period and has them all dealt with in a single court hearing, so only has to make a single hardship plea.
An example of (b) would be a case I read about on a solicitor's blog of an HGV driver who failed to notice a temporary speed limit on a road he obviously drove a lot, and by the time the first NIP arrived he'd already been caught 9 times by the same set of average speed cameras. Is that ban-worthy? The magistrates obviously thought not, and let him keep driving despite his 27 points. Another hypothetical example would be a person who gets home from several months abroad and finds that the person he left the car with has been driving like a knob, that there are 5 unopened NIPs on the doormat and that the deadline for replying to them has already passed... But of course, the full details of cases like that wouldn't make as good a headline as "driver with a squillion points keeps licence"