Why are so many americans on Omeprazole/Prilosec? (or am I missing something)

I've bee in the US for 2 years and I've lived in a few countries and travelled extensively for 30+ years.
I have never seen so many ads, and easy of availability for heartburn/indigestion med. Like at Costco, it seems like its a very popular item. But I dont recall ever seeing this much sales in any other country I have lived in.
I get the ads are a USA unique thing, but wtf are people eating here that they arent in countries around it?