It’s not a universal truth that you can just choose to get a vaccination without making an appointment or needing to involve insurance etc.
In a hypothetical extreme scenario, imagine having to weigh the risks between getting the vaccine that will potentially save your life and unexpectedly getting an appointment reminder text/email or follow-up contact that alerts the controlling partner and they potentially end your life for the “transgression.”
The vaccine being “cheap” is also not universal and if you aren’t allowed personal discretionary spending anything >$0 isn’t cheap enough.