They often appear out of nowhere during commercials.

Haven’t seen commercials in many years so I didn’t know commercials had QR codes in them. What is the reason to engage with them? Discount codes?

Yes, among other things; also more information about the product being advertised.

This reminds me of a pamphlet I got that had just a giant QR code on it related to a specific disease. The rest of the pamphlet had keywords and cloud bubbles or pictures of people.

The QR code leads to a page that has more information, but they put ZERO information on the pamphlet even though it could have conveyed all the information behind the QR code quite well and look good still.

I don't use QR codes because it is usually information that is useless. Or it would be on the actual thing.