First of all, social security has a reimbursement rate, usually 75% reimbursement, while commercial insurance can do 100% reimbursement.
Secondly, social security also has clear restrictions on devices and drugs, many imported drugs can not give reimbursement, while high-end medical insurance is not these restrictions, all the brief medical devices, all imported drugs are reimbursed.
Finally, the social security system has only been opened in a few cities, which means that many times when I am in a foreign country, my social security system can not be used, while the commercial insurance not only solves the problem of foreign medical treatment, but also can be reimbursed even if I am in a foreign country.
The above is just some theoretical elaboration, you can add some data to the above three points to form their own words, I hope it can help you.
Extended reading: insurance how to buy, which is good, hand to teach you to avoid the insurance of these "pits"