If you walk into a high end bike shop you won't see many steel bikes, you'll see them mostly with higher end materials like aluminum, titanium, or carbon fiber.

Most people aren't getting their bikes from a high end bike shop though, most are getting their bikes from discount shops like Walmart, which sells mostly steel bikes.

First result on Google is steel:

https://www.walmart.com/ip/Kent-Bicycles-27-5-in-Male-Sea-Ch...