Because they're idiots.
There are some cool ones now that look more like real bracelets. It's worth investing in one. I wear mine all the time and nobody knows.
A possible answer for rude people is "Don't you just love it? It's one of my favorite pieces of jewelry".

Idiots

Even after my brain surgery, I still wear my Medic Alert necklace. I keep them updated. I am now more than 11 years seizure-free and on fewer medicines, but if there were an issue and I were unconscious, I want the EMS to know what has been done and how to react. Never give up.

Don’t be afraid to wear the medical ID Bracelet. Most people doesn’t understand what people with epilepsy are going through. If they was to have epilepsy then they would feel everything that all the people living with epilepsy is going through

I ware mine all the time because it's good that the medical personal know what meds you take and just to be aware.

They are total morons. Did you smack them upside the head with a baseball bat and ask them why people with allergies, with MS, with kidney issues, or any number of other conditions wear MedicAlert bracelets?? I wish I had mine on when the EMT's took me to the ER & the residents manning the place gave me drugs that I was allergic to and misdiagnosed my epilepsy as a stroke. That tells you how F'd up people are, they don't think unless they have it (the MedicAlert bracelet) !!! Oh. Well I guess that means they really can't think because they have to have it spelled out for them. God help us if some of these make it to become MD's