It's because their approach to protests is to form police lines. They want to form a phalanx-style wall of police that cuts off access to the road. This limits freedom of movement and lets them direct the protest towards a given direction if they decide to break it up and fire tear gas into the crowd.
They probably don't have enough people to form 10 police lines.
I would call this "decentralized protest" and yes it cripples the current tactics of the police.
Their answer will be decentralized policing, basically nazi tactics. Informants, tip lines, rewards for ratting our your neighbor. The FBI uses the same type of tactic when they do manhunts. Except they will use these tactics to target the people organizing the protests.