1. Doctors estimate how good the insurance is.
2. If it is good they create a huge bill.
3. Health insurance negotiates the discount and it can be big.
4. Regardless of your insurance you pay plus/minus the same.
Why? Unclear.
About being in US for a long time and not having the insurance.
I like rock climbing, skiing, snowboarding. The chance of an accident in these sports is rather high. I would feel uncomfortable doing them without insurance.