people do get admitted to ICU due to severe illness but also ICU can be an overflow if there are no monitored beds available on the acute care/coronary care unit, and vice a versa...
You can remain naive if you like. I could give a number of situation/stories. Here’s one.
At a certain doctor owned/run hospital, when the doctor returned from vacation he was upset to learn the number of empty beds. The next day, as he began to see new patients at his general practice, he was committed to admit new hospital patients as fast as he could. Those beds needed to filled lickety-split. A certain nurse, friend, knew what he was doing. She shared the following bit (in her words).
“I came out and saw this older gentleman walk back in, and I asked, “Did you find the admittance office?”, he said, “Oh yes, but they told me to come back to see the doctor because I don’t have insurance.”
She said the doctor walked out to where they were, and the doctor asked, “What happened, did you find the admittance office?”, “Yes sir”, he responded, “but they wouldn’t admit me because I don’t have insurance.” The doctor replied, “Let me review my notes...oh yes...it’s alright, you can go on home. I’ll give you a prescription, and you should be fine.”