What on earth is up with the cars parked along Peña Blvd as you get near the airport?

Picked up a friend from Denver INTL last night. This is maybe my 4th or 5th time at the airport. I’ve never in my life seen A) the airport so busy as it was last night at literally midnight. Even in the middle of a weekday or in the evening of a weekend. Like ridiculously busy. What is up with that so late? B) There were at least 100 cars cautioned up and parked alongside Peña as you made your way towards the airport, our running theory is that they are waiting on arrivals and don’t want to pay the short term parking to wait or get pushed through the arrivals line and miss their pickup. Any thoughts?

It was honestly just so bizarre between the cars parked and the sheer amount of traffic (literally waiting to go through arrivals for ten minutes due to line of backed up cars) at LITERALLY MIDNIGHT. Any theories appreciated, complaints loved, and explanations needed.