When you use your car, you trust 100 different manufacturers from all corners of the earth. When you go to the hospital, you trust 100 different machines, chemicals, gloves, needles etc. It's no different.
When I use a car I trust the combination of the manufacturer and the regulator to have used parts in a fashion such that they won't kill me. I don't know or trust the individual part manufacturers, that's the automakers job.
There is no equivalent to the doctor, or the automaker, or the regulator here. It is not at all similar.
There is no FDA or NHTSA for web technologies.
Similar for the car manufacture, plus there are negligence laws in place if either the hospital suppliers or car manufacturers fail.