Major airlines like United want to keep their contractors financially dependent, but don’t want to take on the costs of operating feeder flights with their own higher-paid employees. Contracting out these flights enables airlines to evade their union contracts and create a de facto two-tier wage scale, with contractors’ employees paid less than the union scale for mainline airline employees. United wants Republic to emerge from bankruptcy and keep flying, which probably depends on Republic dodging the bullet of blame for this incident.
The police who responded have police powers but aren’t part of the Chicago Police Department. That’s not as strange as you might think. Many of the people wearing United Airlines uniforms at many airports don’t work for United. Most of the people wearing TSA uniforms at SFO don’t work for the TSA — they work for Covenant Aviation Security. Similarly, many of the people with badges patrolling airports aren’t regular police, or aren’t the ones you would expect.