According to the well-publicized replay rules, on-field decisions will only be overturned if there is "clear and obvious visual evidence" warranting change. Clear and obvious visual evidence does not include camera angles in which the ball or participants in question (feet or knees, for example) are partially obscured.
Such was the case on the Jones review, NFL Network Insider Ian Rapoport reported, per a source informed of the situation. Per the source, NFL head of officiating Al Riveron could not tell on the overhead broadcast camera angle if the ball touched the ground prior to Jones gaining control of it, and in the other angles, the ball was at least partially obscured in all of them. An obscured ball removes the chance of finding "clear and obvious visual evidence," making an overturn impossible.
It's just the first of what will likely be many fine print moments of 2018. After all, we just emerged from a decade-long battle with defining what is and isn't a catch, and Thursday night didn't exactly smooth over that frayed subject. At the very least, though, this explanation helps bring some sense to what seemed almost inexplicable on Thursday night.