This is obviously intentional, and in many parts of the US totally legal. I don't know specific Colorado laws but there is no federal law against this.
Scheduling is not an issue, and there is no need to waste an ED's time on such things. Some urgent care spots specifically have a "doctors note" service.
It doesn't make the policy any better (I've worked such jobs), but I don't think there is a need to exaggerate how the process works in real life.
An airport subcontractor came to us having issues with getting enough baggage workers. Issue was they paid minimum wage, were located 30 minutes outside the city, and there was no public transport. There was no way for the workers to get to the job! The narrative was "these worker are so untrustworthy/lazy/full of excuses." So they would pay a 50% to an agency hoping gig-contractors could save them on single-day contracts rather than just putting that money to better wages or transit perks.
Contempt really does describe the management attitudes I ran into.
It's worse than contempt, it's abuse. He is looking for ways to make recovery from illness more difficult than it needs to be, and in turn hope some will come to work when they can't get a "regular" doctor visit in time - during a holiday week.
It looks like this is not a fun week for anyone who works at Southwest.
1. Hiring more people (more than 3 days in advance).
2. Paying people more so they don't quit.
3. Giving people paid sick time and not threatening their jobs when they take it so that they don't come to work sick and get a bunch of their colleagues sick.
4. Selling fewer tickets and running fewer flights if you don't have enough capacity to support the current workload.