...and then you leave a safe distance behind that car.
Jesus Christ people. It's like you guys don't know how to drive the speed limit like the law abiding citizens.
Driving to St. Louis every morning from Illinois I can tell you that leaving a safe gap equals something just merging into that gap, and then you if you leave a safe gap again, someone else just merges into that space. Either way the driver behind you gets pissed because you're not letting them pass but you're letting people get in front of you.
It's a never ending battle, and a major reason why states, including Illinois, have very specific laws about it. One of the reasons you're supposed to get out of the left lane is because traffic behind you wants to pass, and that means someone is closing distance on you and if you don't move, they're going to get close to you. Think of it like camping at a stop sign. Of course the guy behind you is tailgating. It's because he's waiting on you to go.
I know in Illinois, the brake-checker could have received a citation for that and likely would be told they should have moved into the right lane prior to the interchange. Illinois' law is pretty strict about the left lane. You have 1/4 mile to make a pass in the left lane before you're required to get out of it. It also states you must cede the left lane to passing traffic immediately.
The left lane driver was obstructing faster traffic and that was made obvious because he brake checked in a situation that he caused. Had he not brake checked, he could have simple moved over after the interchange and then let the driver go around him. But by brake checking, he deliberately obstructed traffic. In Illinois, that's a citation.
The tailgater would have also been cited though.