Hell, they had videotape of Bryant hitting then killing Darcy Shepard, and the crown didn't have enough evidence to peruse charges.
The Crown withdrew charges because it felt it didn't have a reasonable chance of conviction. Big difference, in legal terms.
A witness came forward with photographs of Shepard attacking a motorist in the exact same manner as Bryant alleged he was attacked.
Bryant's lawyer shared those photographs with the Crown; she was under no obligation to do so and in fact took a huge risk doing so.
The Crown considered all the evidence and decided that it was in everyone's best interest to withdraw the charges.
To the best of my knowledge (and I'm no expert but I did read about it extensively) there is no videotape of Bryant hitting or killing Shepard. At best, there would be video, if there is any video, of Shepard assaulting Bryant, hanging onto the steering wheel, and ulimately and tragically striking a stationary object on the sidewalk as he forced the vehicle to turn into the curb.
Bryant then immediately pulled into a hotel and used the phone to call 911, then waited for the police.
Far cry from causing a completely passive passenger to fall off, then flee, abandoning her to be killed by traffic, and avoiding police for three weeks.