You can bet I shower daily. Sometimes I shower several times a day (although fortunately I live by the sea so I try to jump in there instead when possible). I also sometimes go though several shirts in a day and have to take care to manage my electrolytes and hydration.
Showering this often is not a luxury, it's a necessity. To avoid becoming a stinking sweat monster who would send children screaming, I mean.
Locals don't have this problem. I've been living here for years and I don't think my body is going to adapt.
America is a big place, and a lot of it is hot and populated with many people of a similar ancestry to mine. Maybe it's where their "obsession" comes from?