A study released on Monday has the details:
The two major issues we have uncovered are the enforcement of traveling and blocking that we articulate in depth.
In a nutshell, missed traveling calls have become a bigger issue through the years because many players have become adept at manipulating the ball as they complete their dribble to sneak in an extra step or half-step before taking the two steps they’re allowed to take. For some reason, we’ve seen announcers and even NBA officials refer to this as ‘the gather,’ but one problem is that the word ‘gather’ is not in the rulebook!
To me, it makes sense that NBA refs miss a higher percentage of calls than their counterparts in other sports: professional basketball is fast-moving, with fewer starts and stops, and there seem to be more judgment calls on every play. [The easiest comparison to make would be holding calls in the NFL, but there are more officials looking out for that and it's just one of a number of clearer calls that the refs can make.]
Nonetheless, the scourge of uncalled traveling haunts the NBA. Many older fans are turned off by perceived superstar treatment and the idea that the NBA game is somehow impure (just ask anyone who prefers the college game). What is clear is that there absolutely needs to be an even enforcement of the rules. The aforementioned researcher notes this, asking “Is it fair to players who follow the rules?”