Many people traveling to a theme park want to experience the heavily-advertised new ride. Because many of these guests are repeat visitors, they are willing to devote more of their days to seeing the new ride, even at the expense of other attractions, which they have seen before. Many guests may not even be aware that they need to "join a boarding group" prior to arriving, meaning they miss out on one of their only opportunities to get access. Others are aware there isn't a regular line but are not familiar with the system, are not technologically adept, or may not even have the sharp motor functions to do the "fast taps" required to succeed.
Even if you do "everything right," which is in no way a given, you can still be denied access. It's an anti-guest system, and it's embarrassing that anyone here is defending it.